Transmission structure and working vehicle

ABSTRACT

In a transmission structure according to this invention, speed change ratios of input side first and second transmission mechanisms are set so that the rotational speed of a planetary second element is the same when an HST output is set to a second HST speed in either a first transmission state or a second transmission state, and the rotational speed of a planetary first element is the same when the HST output is set to the second HST speed in either the second transmission state or the first transmission state. The speed change ratios of an output side first and second transmission mechanisms are set so that the rotational speed developed in a speed change output shaft when the HST output is set to the second HST speed is the same in either the first or second transmission states.

TECHNICAL FIELD

The present invention relates to a transmission structure including ahydromechanical transmission structure (HMT structure) that has ahydrostatic transmission (HST) and a planetary gear mechanism, and aworking vehicle provided with the transmission structure.

BACKGROUND ART

The HMT structure containing a combination of the HST and the planetarygear mechanism has been suitably used for a traveling systemtransmission path of working vehicles, such as a combine and a tractor,for example. Further, various configurations for expanding the vehiclespeed variable range in the working vehicle provided with the HMTstructure have also been proposed.

For example, Japanese Patent No. 5822761 (hereinafter referred to asPatent Document 1) discloses a combine in which the HMT structure and amultistage speed change structure having three speed change stages of alow speed stage, an intermediate speed stage, and a high speed stage aredisposed in series in a traveling system transmission path, whereby thevehicle speed variable range is extended.

However, the configuration described in Patent Document 1 assumes that aspeed change operation of the multistage speed change structure isperformed in advance before starting the traveling of a vehicle, andthus, when the speed change operation of the multistage speed changestructure is performed during the vehicle traveling, the followinginconveniences arise.

This point is described taking, as an example, a case where the HMTstructure is operated to increase the traveling vehicle speed in a statewhere the multistage speed change structure is engaged with the lowspeed stage, and, when the traveling vehicle speed reaches apredetermined vehicle speed, the multistage speed change structure isspeed-changed from the low speed stage to the intermediate speed stage.

In this case, in a stage where an output of the HMT structure reachesthe maximum speed or around the maximum speed in the low speed stageengagement state of the multistage speed change structure, themultistage speed change structure is shifted from the low speed stage tothe intermediate speed stage while the output of the HMT structure ismaintained at the maximum speed or around the maximum speed, whichcauses a significant vehicle speed change in speed changing, so that theride comfort reduces and an excessive load is applied to the travelingsystem transmission path.

With respect to this point, Japanese Patent No. 4162328 (hereinafterreferred to as Patent Document 2) proposes a working vehicletransmission in which the HMT structure and the multistage speed changestructure are disposed in series in the traveling system transmissionpath and which can suppress a vehicle speed change to prevent theapplication of an excessive load to the traveling system transmissionpath even when the multistage speed change structure is speed-changedduring the vehicle traveling.

In detail, the transmission described in Patent Document 2 is providedwith the HMT structure having the HST and the planetary gear mechanism,the multistage speed change structure speed-changing the output of theHMT structure in multiple stages, and a lock-up mechanism.

The HST has a pump inputting rotation power from a driving source, amotor fluidly driven by the pump, and an output adjustment membervarying the capacity of at least one of the pump and the motor (forexample, pump), in which the output adjustment member operates accordingto the operation amount of a speed change operation member which ismanually operated, so that the rotational speed of the motorcontinuously changes in response to the operation.

The planetary gear mechanism is configured to synthesize rotation powerfrom the HST input into a sun gear and rotation power from a drivingsource input into the carrier, and output the synthesized rotation powerfrom an internal gear toward the multistage speed change structure.

The lock-up mechanism is configured to synchronously rotate the carrierand the internal gear only during a speed change period of themultistage speed change structure.

The speed change operation of the transmission described in PatentDocument 2 is described taking a case where the multistage speed changestructure is accelerated from a first speed stage to a second speedstage as an example.

When the speed change operation member is operated in a accelerationdirection within the first speed stage operation range, the outputadjustment member is moved in a direction of changing the speed from afirst HST speed (for example, reverse rotation side maximum speed) to asecond HST speed (for example, normal rotation side maximum speed).

Then, when the speed change operation member is operated to a boundaryposition between the first speed stage operation range and a secondspeed stage operation range, the output adjustment member is operated toa second HST speed position (for example, normal rotation side maximumtilted position), so that an HST output is brought into the second HSTspeed (for example, normal rotation side maximum speed).

This state is the maximum speed output state of the HMT structure in afirst speed stage engagement state of the multistage speed changestructure.

When the speed change operation member is operated to the second speedstage operation range beyond the boundary position between the firstspeed stage operation range and the second speed stage operation range,the speed of the multistage speed change structure is accelerated fromthe first speed stage to the second speed stage in response to theoperation.

In the speed change period of the multistage speed change structure, theinternal gear and the carrier are coupled by the lock mechanism to besynchronously rotated as described above.

Thus, the rotation power synchronized with the rotation power from thedriving source input into the carrier is transmitted to the multistagespeed change structure to which the rotation power from the internalgear is input.

Meanwhile, in the speed change period of the multistage speed changestructure, the output adjustment member is brought into a free statewhere the connection with the speed change operation member is canceled.Therefore, a motor shaft and the sun gear which are operatively coupledwith each other are rotated at a rotational speed (hereinafter referredto as “speed change period rotational speed”) defined by the rotationalspeed of the internal gear and the carrier which are coupled by the lockmechanism to be synchronously rotated with the rotation power from thedriving source.

Thus, the output adjustment member is returned from the second HST speedposition (for example, normal rotation side maximum tilted position) toa position where an HST output corresponding to the speed change periodrotational speed of the sun gear is developed (hereinafter referred toas “speed change period reference position”) in a direction toward thefirst HST speed position.

Thereafter, when the speed change operation member is operated in theacceleration direction within the second speed stage operation range,the output adjustment member is operated from the speed change periodreference position toward the second HST speed position, so that therotational speed of the motor shaft is accelerated.

Thus, the rotational speed of the sun gear rotationally driven by theHST output from the motor shaft is accelerated, so that the rotationalspeed of the internal gear is accelerated.

As described above, in the transmission described in Patent Document 2,the rotation power input into the sun gear in the speed change operationof the multistage speed change structure is reduced from the second HSTspeed (for example, normal rotation side maximum speed) to the speedchange period rotational speed.

Although the transmission described in Patent Document 2 having such aconfiguration is useful in the point that the change width of thetraveling vehicle speed in the speed change of the multistage speedchange structure can be suppressed as compared with the configurationdescribed in Patent Document 1, a certain large degree of speed changehas still remained in the traveling vehicle speed in the speed change ofthe multistage speed change structure.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-describedconventional technique. It is a first object of the present invention toprovide a transmission structure having an HST and a planetary gearmechanism and a speed change output shaft operatively driven by anoutput portion of the planetary gear mechanism and capable of extendingthe speed change width of the speed change output shaft without causinga rapid rotational speed change in the speed change output shaft.

Moreover, it is a second object of the present invention to provide aworking vehicle provided with the transmission structure.

In order to achieve the first object, a first aspect of the presentinvention provides a transmission structure including: an HSTcontinuously changing rotation power operatively input into a pump shaftfrom a driving source to rotation power at least between a first HSTspeed and a second HST speed according to an operation position of anoutput adjustment member, and then outputting the changed rotation poweras an HST power from a motor shaft; a planetary gear mechanism havingfirst to third elements, in which the third element functions as aninput portion of the HST output; a speed change output shaft; an inputside first transmission mechanism capable of operatively transmittingthe rotation power of the driving source to the first element at aninput side first speed change ratio; an input side second transmissionmechanism capable of operatively transmitting the rotation power of thedriving source to the second element at an input side second speedchange ratio; input side first and second clutch mechanismsengaging/disengaging power transmission of the input side first andsecond transmission mechanisms, respectively; an output side firsttransmission mechanism capable of operatively transmitting the rotationpower of the second element to the speed change output shaft at anoutput side first speed change ratio; an output side second transmissionmechanism capable of operatively transmitting the rotation power of thefirst element to the speed change output shaft at an output side secondspeed change ratio; output side first and second clutch mechanismsengaging/disengaging power transmission of the output side first andsecond transmission mechanisms, respectively; a speed change operationmember; an HST sensor directly or indirectly detecting a speed changestate of the HST; an output sensor directly or indirectly detectingrotational speed of the speed change output shaft; and a control devicecontrolling operations of the output adjustment member, the input sidefirst and second clutch mechanisms, and the output side first and secondclutch mechanisms. In the first aspect of the present invention, basedon detection signals of the HST sensor and the output sensor, while thecontrol device develops a first transmission state where the firstelement is functioned as an input portion of reference power operativelytransmitted from the driving source and the second element is functionedas an output portion of synthetic rotation power by bringing the inputside and output side first clutch mechanisms into an engagement stateand bringing the input side and output side second clutch mechanismsinto a disengagement state in a low speed state where the rotationalspeed of the speed change output shaft is less than a predeterminedswitching speed, the control device operates the output adjustmentmember so that the HST output is speed-changed from the first HST speedtoward the second HST speed in response to an acceleration operation ofthe speed change operation member, and meanwhile, while the controldevice develops a second transmission state where the first element isfunctioned as the output portion and the second element is functioned asthe input portion of the reference power by bringing the input side andoutput side first clutch mechanisms into the disengagement state andbringing the input side and output side second clutch mechanisms intothe engagement state in a high speed state where the rotational speed ofthe speed change output shaft is equal to or higher than the switchingspeed, the control device operates the output adjustment member so thatthe HST output is speed-changed from the second HST speed toward thefirst HST speed in response to the acceleration operation of the speedchange operation member. The input side first and second speed changeratios are set so that rotational speed of the second element when theHST output is set to the second HST speed in the first transmissionstate and rotational speed of the second element by rotation powertransmitted through the input side second transmission mechanism in thesecond transmission state are same and so that rotational speed of thefirst element when the HST output is set to the second HST speed in thesecond transmission state and rotational speed of the first element byrotation power transmitted through the input side first transmissionmechanism in the first transmission state are same. The output sidefirst and second speed change ratios are set so that rotational speeddeveloped in the speed change output shaft when the HST output is set tothe second HST speed is same in the first and second transmissionstates.

The transmission structure according to the first aspect can develop thefirst transmission state where the speed change output shaft isincreased to the switching speed as the HST output is speed-changed fromthe first HST speed to the second HST speed and the second transmissionstate where the speed change output shaft is increased from theswitching speed as the HST output is speed-changed from the second HSTspeed to the first HST speed to thereby expand the speed changeablerange (speed change region) of the speed change output shaft, andfurther can effectively prevent or reduce the rotational speeddifference in the speed change output shaft at the timing of switchingbetween the first and second transmission states.

In order to achieve the first object, a second aspect of the presentinvention provides a transmission structure including an HSTcontinuously changing rotation power operatively input into a pump shaftfrom a driving source to rotation power at least between a first HSTspeed and a second HST speed according to an operation position of anoutput adjustment member, and then outputting the changed rotation poweras an HST output from a motor shaft; a planetary gear mechanism havingfirst to third elements, in which the third element functions as aninput portion of the HST output; a speed change output shaft; an inputside first transmission mechanism capable of operatively transmittingthe rotation power of the driving source to the first element at aninput side first speed change ratio; an input side second transmissionmechanism capable of operatively transmitting the rotation power of thedriving source to the second element at an input side second speedchange ratio; input side first and second clutch mechanismsengaging/disengaging power transmission of the input side first andsecond transmission mechanisms, respectively; output side first andsecond clutch mechanisms engaging/disengaging power transmission fromthe second element and the first element, respectively, to the speedchange output shaft; a speed change operation member; an HST sensordirectly or indirectly detecting a speed change state of the HST; anoutput sensor directly or indirectly detecting rotational speed of thespeed change output shaft; and a control device controlling operationsof the output adjustment member, the input side first and second clutchmechanisms, and the output side first and second clutch mechanisms,wherein based on detection signals of the HST sensor and the outputsensor, while the control device develops a first transmission statewhere the first element is functioned as an input portion of referencepower operatively transmitted from the driving source and the secondelement is functioned as an output portion of synthetic rotation powerby bringing the input side and output side first clutch mechanisms intoan engagement state and bringing the input side and output side secondclutch mechanisms into a disengagement state in a low speed state wherethe rotational speed of the speed change output shaft is less than apredetermined switching speed, the control device operates the outputadjustment member so that the HST output is speed-changed from the firstHST speed toward the second HST speed in response to an accelerationoperation of the speed change operation member and meanwhile, while thecontrol device develops a second transmission state where the firstelement is functioned as the output portion and the second element isfunctioned as the input portion of reference power by bringing the inputside and output side first clutch mechanisms into the disengagementstate and bringing the input side and output side second clutchmechanisms into the engagement state in a high speed state where therotational speed of the speed change output shaft is equal to or higherthan the switching speed, the control device operates the outputadjustment member so that the HST output is speed-changed from thesecond HST speed toward the first HST speed in response to theacceleration operation of the speed change operation member, and theinput side first and second speed change ratios are set so thatrotational speed of the second element when the HST output is set to thesecond HST speed in the first transmission state and rotational speed ofthe second element by rotation power transmitted through the input sidesecond transmission mechanism in the second transmission state are sameand so that rotational speed of the first element when the HST output isset to the second HST speed in the second transmission state androtational speed of the first element by rotation power transmittedthrough the input side first transmission mechanism in the firsttransmission state are same.

The transmission structure according to the second aspect can developthe first transmission state where the speed change output shaft isincreased to the switching speed as the HST output is speed-changed fromthe first HST speed to the second HST speed and the second transmissionstate where the speed change output shaft is increased from theswitching speed as the HST output is speed-changed from the second HSTspeed to the first HST speed to thereby expand the speed changeablerange (speed change region) of the speed change output shaft, andfurther can effectively prevent or reduce the rotational speeddifference in the speed change output shaft at the timing of switchingbetween the first and second transmission states.

In the second aspect, the control device preferably may operate, inswitching between the first and second transmission states, the outputadjustment member so that rotational speed developed in the speed changeoutput shaft in a transmission state after the switching coincides withor approaches rotational speed developed in the speed change outputshaft in a transmission state before the switching.

In any one of the various configurations according to the first andsecond aspects, in a switching transition stage between the first andsecond transmission states, a double transmission state preferably maybe developed in which both the input side first and second clutchmechanisms are brought into the engagement state and both the outputside first and second clutch mechanisms are brought into the engagementstate.

In one embodiment capable of developing the double transmission state,at least one of an input side clutch unit formed by the input side firstand second clutch mechanisms and an output side clutch unit formed bythe output side first and second clutch mechanisms is configured as adog clutch type.

The clutch unit of the dog clutch type has a slider supported by acorresponding rotation shaft so as not to be relatively rotatable and soas to be movable in an axial direction and first and secondrecess-projection engagement portions on one side and another side,respectively, in the axial direction.

When the slider is located at a first position on the one side in theaxial direction, the first recess-projection engagement portion isengaged with a corresponding recess-projection engagement portion whilethe second recess-projection engagement portion is not engaged with acorresponding recess-projection engagement portion, whereby the sliderbrings only the first clutch mechanism into the engagement state, whenthe slider is located at a second position on the another side in theaxial direction, the second recess-projection engagement portion isengaged with a corresponding recess-projection engagement portion whilethe first recess-projection engagement portion is not engaged with acorresponding recess-projection engagement portion, whereby the sliderbrings only the second clutch mechanism into the engagement state, andwhen the slider is located at an intermediate position between the firstand second positions with respect to the axial direction, both the firstand second recess-projection engagement portions are engaged withcorresponding recess-projection engagement portions, whereby the sliderbrings both first and second clutch mechanisms into the engagementstate.

The input side first transmission mechanism may have an input side firstdriving gear relatively rotatably supported by a main driving shaftoperatively coupled with the driving source and an input side firstdriven gear operatively coupled with the input side first driven gearand made relatively unrotatable to the first element, and the input sidesecond transmission mechanism may have an input side second driving gearrelatively rotatably supported by the main driving shaft and an inputside second driven gear operatively coupled with the input side seconddriving gear and made relatively unrotatable to the second element.

In this embodiment, the input side clutch unit may be configured as thedog clutch type and having an input side slider as the slider.

The input side slider is supported by the main driving shaft between theinput side first and second driving gears so as not to be relativelyrotatable and so as to be movable in the axial direction, when locatedat the first position, the first recess-projection engagement portion isengaged with a recess-projection engagement portion of the input sidefirst driving gear while the second recess-projection engagement portionis not engaged with a recess-projection engagement portion of the inputside second driving gear, whereby the input side slider brings only theinput side first clutch mechanism into the engagement state, whenlocated at the second position, the second recess-projection engagementportion is engaged with the recess-projection engagement portion of theinput side second driving gear while the first recess-projectionengagement portion is not engaged with the recess-projection engagementportion of the input side first driving gear, whereby the input sideslider brings only the input side second clutch mechanism into theengagement state, and, when located at an intermediate position, thefirst and second recess-projection engagement portions are engaged withthe recess-projection engagement portions of the input side first andsecond driving gears, respectively, whereby the input side slider bringsboth the first and second clutch mechanisms into the engagement state.

The transmission structure according to the first aspect may furtherinclude

a speed change intermediate shaft coupled with the second element so asnot to be relatively rotatable around an axis, and the first element maybe relatively rotatably supported by the speed change intermediateshaft.

In this case, the output side first transmission mechanism has an outputside first driving gear supported by the speed change intermediate shaftso as not to be relatively rotatable and an output side first drivengear operatively coupled with the output side first driving gear andrelatively rotatably supported by the speed change output shaft. Theoutput side second transmission mechanism has an output side seconddriving gear coupled with the first element so as not to be relativelyrotatable and an output side second driven gear operatively coupled withthe output side second driving gear and relatively rotatably supportedby the speed change output shaft. The output side first and secondclutch mechanisms have recess-projection engagement portions provided inthe output side first and second driven gears and an output side slidersupported between the output side first and second driven gears by thespeed change output shaft so as not to be relatively rotatable and so asto be movable in an axial direction and provided with first and secondrecess-projection engagement portions on one side and another side,respectively, in the axial direction.

When the output side slider is located at a first position on the oneside in the axial direction, the first recess-projection engagementportion is engaged with a recess-projection engagement portion of theoutput side first driven gear while the second recess-projectionengagement portion is not engaged with a recess-projection engagementportion of the output side second driven gear, whereby the output sideslider brings only the output side first clutch mechanism into theengagement state, when the output side slider is located at a secondposition on the another side in the axial direction, the secondrecess-projection engagement portion is engaged with therecess-projection engagement portion of the output side second drivengear while the first recess-projection engagement portion is not engagedwith the recess-projection engagement portion of the output side firstdriven gear, whereby the output side slider brings only the output sidesecond clutch mechanism into the engagement state, and, when the outputside slider is located at an intermediate position between the firstdirection and the second direction in the axial direction, the first andsecond recess-projection engagement portions are engaged with therecess-projection engagement portions of the output side first andsecond driven gears, respectively, whereby the output side slider bringsboth the output side first and second clutch mechanisms into theengagement state.

In another embodiment capable of developing the double transmissionstate, at least one of an input side clutch unit formed by the inputside first and second clutch mechanisms and an output side clutch unitformed by the output side first and second clutch mechanisms may beconfigured as a hydraulic friction plate type developing a clutchengagement state by receiving pressure oil supply.

The transmission structure according to this embodiment is furtherprovided with a pressure oil supply line receiving pressure oil supplyfrom a hydraulic source, first and second supply/discharge linessupplying/discharging pressure oil to the first and second clutchmechanisms, respectively, in the clutch units of the hydraulic frictionplate type, first and second electromagnetic valves which are interposedin the first and second supply/discharge lines, respectively, and whichcan take a discharge position where a corresponding supply/dischargeline is drained and a supply position where a correspondingsupply/discharge line is fluid-connected to the pressure oil supplyline, and a clutch engagement detection unit detecting an engagementstate of the first and second clutch mechanisms in the clutch units ofthe hydraulic friction plate type.

The control device locates the first electromagnetic valve at the supplyposition and locates the second electromagnetic valve at the dischargeposition to develop the first transmission state in the low speed statewhere the rotational speed of the speed change output shaft is less thanthe switching speed, while locating the first electromagnetic valve atthe discharge position and locating the second electromagnetic valve atthe supply position to develop the second transmission state in the highspeed state where the rotational speed of the speed change output shaftis equal to or higher than the switching speed. Also, the control devicemoves the electromagnetic valve located at the discharge position attime before the switching from the discharge position to the supplyposition while maintaining the electromagnetic valve located at thesupply position at the time before the switching at the supply positionin the switching between the first and second transmission states, andthen moves the electromagnetic valve located at the supply position atthe time before the switching from the supply position to the dischargeposition after passage of predetermined time from time when recognizingthat the clutch mechanism to which pressure oil is supplied through theelectromagnetic valve, a position of which is moved from the dischargeposition to the supply position is brought into the engagement statebased on a signal from the clutch engagement detection unit.

Preferably, the first and second electromagnetic valves may beconfigured as proportional electromagnetic valves configured to receivehydraulic pressure of corresponding supply/discharge lines as pilotpressure to thereby maintain the hydraulic pressure of the correspondingsupply/discharge lines in a state where a position signal from thecontrol device to the supply position is input at an engagementhydraulic pressure.

In the first and second aspects of the present invention, the input sidefirst and second clutch mechanisms may be configured as a hydraulicfriction plate type developing a clutch engagement state by receivingpressure oil supply.

In this case, the transmission structure is provided with a pressure oilsupply line receiving pressure oil supply from a hydraulic source, inputside first and second supply/discharge lines supplying/dischargingpressure oil to the input side first and second clutch mechanisms,respectively, input side first and second electromagnetic valves whichare interposed in the input side first and second supply/dischargelines, respectively, and which can take a discharge position where acorresponding supply/discharge line is drained and a supply positionwhere a corresponding supply/discharge line is fluid-connected to thepressure oil supply line, and a clutch engagement detection unitdetecting an engagement state of the input side first and second clutchmechanisms.

The control device locates the input side first electromagnetic valve atthe supply position and locates the input side second electromagneticvalve at the discharge position in the low speed state where therotational speed of the speed change output shaft is less than theswitching speed, while locating the input side first electromagneticvalve at the discharge position and locating the input side secondelectromagnetic valve at the supply position in the high speed statewhere the rotational speed of the speed change output shaft is equal toor higher than the switching speed. Also, the control device moves theelectromagnetic valve located at the discharge position at time beforethe switching from the discharge position to the supply position whilemaintaining the electromagnetic valve located at the supply position atthe time before the switching at the supply position in the switchingbetween the first and second transmission states, and then moves theelectromagnetic valve located at the supply position at the time beforethe switching from the supply position to the discharge position whenrecognizing that the clutch mechanism to which pressure oil is suppliedthrough the electromagnetic valve, a position of which is moved from thedischarge position to the supply position, is brought into a slidingengagement state based on a signal from the clutch engagement detectionunit.

In the first and second aspects of the present invention, the outputside first and second clutch mechanisms may be configured as a hydraulicfriction plate type developing a clutch engagement state by receivingpressure oil supply.

In this case, the transmission structure is provided with a pressure oilsupply line receiving pressure oil supply from a hydraulic source,output side first and second supply/discharge linessupplying/discharging pressure oil to the output side first and secondclutch mechanisms, respectively, output side first and secondelectromagnetic valves which are interposed in the output side first andsecond supply/discharge lines, respectively, and which can take adischarge position where a corresponding supply/discharge line isdrained and a supply position where a corresponding supply/dischargeline is flued-connected to the pressure oil supply line, and a clutchengagement detection unit detecting an engagement state of the outputside first and second clutch mechanisms.

The control device locates the output side first electromagnetic valveat the supply position and locates the output side secondelectromagnetic valve at the discharge position in the low speed statewhere the rotational speed of the speed change output shaft is less thanthe switching speed, while locating the output side firstelectromagnetic valve at the discharge position and locating the outputside second electromagnetic valve at the supply position in the highspeed state where the rotational speed of the speed change output shaftis equal to or higher than the switching speed. Also, the control devicemoves, in switching between the low speed state and the high speedstate, the electromagnetic valve located at the discharge position attime before the switching from the discharge position to the supplyposition while maintaining the electromagnetic valve located at thesupply position at the time before the switching at the supply position,and then moves the electromagnetic valve located at the supply positionat the time before the switching from the supply position to thedischarge position when recognizing that the clutch mechanism to whichpressure oil is supplied through the electromagnetic valve, a positionof which is moved from the discharge position to the supply position, isbrought into a sliding engagement state based on a signal from theclutch engagement detection unit.

In the first and second aspect of the present invention, the input sidesecond clutch mechanism and the output side second clutch mechanismpreferably may be configured as friction plate clutch mechanisms.

In more preferable configuration, all of the input side first clutchmechanism and the output side first clutch mechanism are configured asfriction plate clutch mechanisms.

The transmission structure according to the present invention mayinclude a pressure oil supply line, an upstream side of which isfluid-connected to a hydraulic source, a drain line, a firstsupply/discharge line supplying/discharging pressure oil to the inputside and output side first clutch mechanisms, a second supply/dischargeline supplying/discharging pressure oil to the input side and outputside second clutch mechanisms, and a switching valve, a position ofwhich is controlled by the control device.

The switching valve is configured to be able to take a first positionwhere the pressure oil supply/discharge line is fluid-connected to thefirst supply/discharge line and the second supply/discharge line isfluid-connected to the drain line and a second position where the firstsupply/discharge line is fluid-connected to the drain line and thepressure oil supply/discharge line is fluid-connected to the secondsupply/discharge line. The input side first and second clutch mechanismsand the output side first and second clutch mechanisms are configured asa hydraulic type engaging power transmission of a correspondingtransmission mechanism by receiving pressure oil supply.

Also, in order to achieve the first object, a third aspect of thepresent invention provides a transmission structure interposed in atraveling system transmission path of a working vehicle including an HSTcontinuously changing rotation power operatively input into a pump shaftfrom a driving source to rotation power at least between a first HSTspeed and a second HST speed according to an operation position of anoutput adjustment member, and then outputting the changed rotation poweras an HST output from a motor shaft; a planetary gear mechanism havingfirst to third elements, in which the third element functions as aninput portion of the HST output; a speed change output shaft; input sidefirst and second transmission mechanisms capable of operativelytransmitting the rotation power of the driving source to the first andsecond elements, respectively; input side and second clutch mechanismsengaging/disengaging power transmission of the input side first andsecond transmission mechanisms, respectively; output side first andsecond clutch mechanisms engaging/disengaging power transmission fromthe second element and the first element, respectively, to the speedchange output shaft; a speed change operation member; an HST sensordirectly or indirectly detecting a speed change state of the HST; anoutput sensor directly or indirectly detecting rotational speed of thespeed change output shaft; and a control device controlling operationsof the output adjustment member, the input side first and second clutchmechanisms, and the output side first and second clutch mechanisms,wherein at least one of an input side clutch unit formed by the inputside first and second clutch mechanisms and an output side clutch unitformed by the output side first and second clutch mechanisms isconfigured as a hydraulic friction plate type developing a clutchengagement state by receiving pressure oil supply, the transmissionstructure is further provided with a pressure oil supply line receivingpressure oil supply from a hydraulic source, first and secondsupply/discharge lines supplying/discharging pressure oil to the firstand second clutch mechanisms, respectively, in the clutch units of thehydraulic friction plate type, first and second electromagnetic valveswhich are interposed in the first and second supply/discharge lines,respectively, and which can take a discharge position where acorresponding supply/discharge line is drained and a supply positionwhere a corresponding supply/discharge line is fluid-connected to thepressure oil supply line, and a clutch engagement detection unitdetecting an engagement state of the first and second clutch mechanismsin the clutch units of the hydraulic friction plate type, wherein basedon detection signals of the HST sensor and the output sensor, in a lowspeed state where the rotational speed of the speed change output shaftis less than a predetermined switching speed, while the control devicedevelops a first transmission state where the first element isfunctioned as an input portion of reference power operativelytransmitted from the driving source and the second element is functionedas an output portion of synthetic rotation power by bringing the inputside and output side first clutch mechanisms into an engagement stateand bringing the input side and output side second clutch mechanismsinto a disengagement state, the control device operates the outputadjustment member so that the HST output is speed-changed from the firstHST speed toward the second HST speed in response to an accelerationoperation of the speed change operation member and meanwhile, in a highspeed state where the rotational speed of the speed change output shaftis equal to or higher than the switching speed, while the control devicedevelops a second transmission state where the first element isfunctioned as the output portion and the second element is functioned asthe input portion of reference power by bringing the input side andoutput side first clutch mechanisms into the disengagement state andbringing the input side and output side second clutch mechanisms intothe engagement state, the control device operates the output adjustmentmember so that the HST output is speed-changed from the second HST speedtoward the first HST speed in response to the acceleration operation ofthe speed change operation member, further, in switching between thefirst and second transmission states, while maintaining one of the firstand second electromagnetic valves located at the supply positions attime before the switching at the supply positions, the control devicemoves another one of the first and second electromagnetic valves locatedat the discharge positions at the time before the switching from thedischarge position to the supply position, and then, when recognizingthat the clutch mechanism to which pressure oil is supplied through theother electromagnetic valve is brought into a sliding engagement statebased on a signal from the clutch engagement detection unit, the controldevice moves the one electromagnetic valve from the supply position tothe discharge position to thereby switch engagement/disengagement of thefirst and second clutch mechanisms in the hydraulic friction plateclutch units.

The transmission structure according to the third aspect makes itpossible to increase a degree of freedom for design to thereby enhanceflexibility in designing device, since it is not needed to strictly setthe speed change ratios of the input side second transmission mechanismand the output side transmission mechanisms for preventing therotational speed difference in the speed change output shaft in shiftingbetween the first and second transmission states. The transmissionstructure according to the third aspect makes it also possible tosuppress unintentional disengagement and reduction of power transmissionin sifting clutch mechanisms under traveling with heavy load.

Also, in order to achieve the first object, a fourth aspect of thepresent invention provides a transmission structure including an HSTcontinuously changing rotation power operatively input into a pump shaftfrom a driving source to rotation power at least between first HST speedand second HST speed according to an operation position of an outputadjustment member, and then outputting the changed rotation power as anHST output from a motor shaft; a planetary gear mechanism having firstto third elements, in which the third element functions as an inputportion of the HST output; a speed change output shaft; input side firstand second transmission mechanisms capable of operatively transmittingthe rotation power of the driving source to the first element and thesecond element, respectively; input side first and second clutchmechanisms engaging/disengaging power transmission of the input sidefirst and second transmission mechanisms, respectively; forward movementfirst and second transmission mechanisms capable of operativelytransmitting rotation power of the second element and the first element,respectively, to the speed change output shaft in a normal rotationstate; a reverse movement transmission mechanism capable of operativelytransmitting the rotation power of the second element to the speedchange output shaft in a reverse rotation state; a forward movementfirst clutch mechanism, a forward movement second clutch mechanism, anda reverse movement clutch mechanism engaging/disengaging powertransmission of the forward movement first transmission mechanism, theforward movement second transmission mechanism, and the reverse movementtransmission mechanism, respectively; a speed change operation member;an HST sensor directly or indirectly detecting a speed change state ofthe HST; an output sensor directly or indirectly detecting rotationalspeed of the speed change output shaft; and a control device controllingoperations of the output adjust member, the input side first clutchmechanism, the input side second clutch mechanism, the forward movementfirst clutch mechanism, the forward movement second clutch mechanism,and the reverse movement clutch mechanism, wherein,

based on detection signals of the HST sensor and the output sensor, in alow speed state where the rotational speed of the speed change outputshaft is from zero speed to speed less than switching speed in a forwardmovement direction, while the control device develops a forward movementfirst transmission state where the input side first clutch mechanism andthe forward movement first clutch mechanism are brought into anengagement state, the control device operates the output adjustmentmember so that the HST output is speed-changed from the first HST speedtoward the second HST speed in response to a forward movement sideacceleration operation of the speed change operation member, in a highspeed state where the rotational speed of the speed change output shaftis equal to or higher than the switching speed in the forward movementdirection, while the control device develops a forward movement secondtransmission state where the input side second clutch mechanism and theforward movement second clutch mechanism are brought into the engagementstate, the control device operates the output adjustment member so thatthe HST output is speed-changed from the first HST speed toward thesecond HST speed in response to the forward movement side accelerationoperation of the speed change operation member, and, in a reversemovement transmission state where the rotational speed of the speedchange output shaft is changed from the zero speed to the reversemovement side, while the control device develops a reverse movementtransmission state where the input side first clutch mechanism and thereverse movement clutch mechanism are brought into the engagement state,the control device operates the output adjustment member so that the HSToutput is speed-changed from the first HST speed toward the second HSTspeed in response to a reverse movement side acceleration operation ofthe speed change operation member.

The transmission structure according to the fourth aspect makes itpossible to develop the forward movement first transmission state wherethe rotational speed of the speed change output shaft is increased inforward movement direction until the switching speed as the HST outputis speed-changed from the first HST speed to the second HST speed, theforward movement second transmission state where the rotational speed ofthe speed change output shaft is increased in forward movement directionfrom the switching speed as the HST output is speed-changed from thesecond HST speed to the first HST speed and the reverse movementtransmission state where the rotational speed of the speed change outputshaft is increased in reverse movement direction as the HST output isspeed-changed from the first HST speed to the second HST speed tothereby expand the speed change range of the speed change output shaft,and further can effectively prevent or reduce the rotational speeddifference in the speed change output shaft in switching between theforward movement first and second transmission states and between theforward movement first transmission state and the reverse movementtransmission state.

In the fourth aspect, the input side first transmission mechanism mayoperatively transmit the rotation power of the driving source to thefirst element at an input side first speed change ratio, and the inputside second transmission mechanism may operatively transmit the rotationpower of the driving source to the second element at an input sidesecond speed change ratio.

In this case, the input side first and second speed change ratios arepreferably set so that rotational speed of the second element when theHST output is set to the second HST speed in the forward movement firsttransmission state and rotational speed of the second element byrotation power transmitted through the input side second transmissionmechanism in the forward movement second transmission state are same andso that rotational speed of the first element when the HST output is setto the second HST speed in the forward movement second transmissionstate and rotational speed of the first element by rotation powertransmitted through the input side first transmission mechanism in theforward movement first transmission state are same.

In the fourth aspect, the forward movement first transmission mechanismmay operatively transmit the rotation power of the second element to thespeed change output shaft at a forward movement first speed change ratioand the forward movement second transmission mechanism may operativelytransmit the rotation power of the first element to the speed changeoutput shaft at a forward movement second speed change ratio.

In this case, the forward movement first and second speed change ratiosare preferably set so that rotational speed developed in the speedchange output shaft when the HST output is set to the second HST speedis same in the first and second transmission states.

In the fourth aspect, the HST and the planetary gear mechanism arepreferably set so that the rotational speed of the second elementbecomes the zero speed when the HST output is set to the first HST speedin the engagement state of the input side first clutch mechanism.

Also, in order to achieve the first object, a fifth aspect of thepresent invention provides a transmission mechanism including an HSTcontinuously changing rotation power operatively input into a pump shaftfrom a driving source to rotation power at least between a first HSTspeed and a second HST speed according to an operation position of anoutput adjustment member, and then outputting the changed rotation poweras an HST output from a motor shaft; a planetary gear mechanism havingfirst to third elements, in which the third element functions as aninput portion of the HST output; a speed change output shaft; an inputside first transmission mechanism capable of operatively transmittingthe rotation power of the driving source to the first element at aninput side first speed change ratio; an input side second transmissionmechanism capable of operatively transmitting the rotation power of thedriving source to the second element at an input side second speedchange ratio; input side first and second clutch mechanismsengaging/disengaging power transmission of the input side first andsecond transmission mechanisms, respectively; an output side firsttransmission mechanism capable of operatively transmitting the rotationpower of the second element to the speed change output shaft at anoutput side first speed change ratio; an output side second transmissionmechanism capable of operatively transmitting the rotation power of thefirst element to the speed change output shaft at an output side secondspeed change ratio; an output side third transmission mechanism capableof operatively transmitting the rotation power of the first element tothe speed change output shaft at an output side third speed change ratiorotating the speed change output shaft at speed higher than the outputside second speed change ratio; output side first to third clutchmechanisms engaging/disengaging power transmission of the output sidefirst to third transmission mechanisms, respectively; a speed changeoperation member; an HST sensor directly or indirectly detecting a speedchange state of the HST; an output sensor directly or indirectlydetecting rotational speed of the speed change output shaft; and acontrol device controlling operations of the output adjustment member,the input side first and second clutch mechanisms, and the output sidefirst to third clutch mechanism, wherein, based on detection signals ofthe HST sensor and the output sensor, in a low speed state where therotational speed of the speed change output shaft is less than a firstswitching speed, while the control device develops a first transmissionstate where the first element is functioned as an input portion ofreference power operatively transmitted from the driving source and thesecond element is functioned as an output portion of synthetic rotationpower by bringing the output side first clutch mechanism into anengagement state and bringing other output side clutch mechanisms into adisengagement state while bringing the input side first clutch mechanisminto the engagement state and bringing the input side second clutchmechanism into the disengagement state, the control device operates theoutput adjustment member so that the HST output is speed-changed fromthe first HST speed toward the second HST speed in response to anacceleration operation of the speed change operation member, in anintermediate speed state where the rotational speed of the speed changeoutput shaft is equal to or higher than the first switching speed andless than a second switching speed, while the control device develops asecond transmission state where the second element is functioned as theinput portion of reference power and the rotation power of the firstelement is operatively transmitted to the speed change output shaft atthe output side second speed change ratio by bringing the output sidesecond clutch mechanism into the engagement state and bringing otheroutput side clutch mechanisms into the disengagement state whilebringing the input side first clutch mechanisms into the disengagementstate and bringing the input side second clutch mechanism into theengagement state, the control device operates the output adjustmentmember so that the HST output is speed-changed from the second HST speedtoward the first HST speed in response to the acceleration operation ofthe speed change operation member, and, in a high speed state where therotational speed of the speed change output shaft is equal to or higherthan the second switching speed, while the control device develops athird transmission state where the second element is functioned as theinput portion of reference power and the rotation power of the firstelement is operatively transmitted to the speed change output shaft atthe output side third speed change ratio by bringing the output sidethird clutch mechanism into the engagement state and bringing otheroutput side clutch mechanisms into the disengagement state whilebringing the input side first clutch mechanism into the disengagementstate and bringing the input side second clutch mechanism into theengagement state, the control device operates the output adjustmentmember so that the HST output is speed-changed from the second HST speedtoward the first HST speed in response to the acceleration operation ofthe speed change operation member, and meanwhile the control deviceoperates the output adjustment member in switching between the secondand third transmission states so that rotational speed developed in thespeed change output shaft in a transmission state after the switchingcoincides with or approaches rotational speed developed in the speedchange output shaft in a transmission state before the switching, andthe input side first and second speed change ratios are set so thatrotational speed of the second element when the HST output is set to thesecond HST speed in the first transmission state and rotational speed ofthe second element by rotation power transmitted through the input sidesecond transmission mechanism in the second transmission state are sameand so that rotational speed of the first element when the HST output isset to the second HST speed in the second transmission state androtational speed of the first element by rotation power transmittedthrough the input side first transmission mechanism in the firsttransmission state are same.

The transmission structure according to the fifth aspect makes itpossible to develop the first transmission state where the rotationalspeed of the speed change output shaft is increased until the firstswitching speed as the HST output is speed-changed from the first HSTspeed to the second HST speed, the second transmission state where therotational speed of the speed change output shaft is increased from thefirst switching speed until the second switching speed as the HST outputis speed-changed from the second HST speed to the first HST speed andthe third transmission state where the rotational speed of the speedchange output shaft is increased from the second switching speed as theHST output is speed-changed from the side of the second HST speed to theside of the first HST speed to thereby expand the speed change range ofthe speed change output shaft, and further can effectively prevent orreduce the rotational speed difference in the speed change output shaftin switching between the first and second transmission states andbetween the second and third transmission states.

The transmission structure according to the fifth aspect may include aspeed change intermediate shaft coupled with the second element so asnot to be relatively rotatable around an axis, and a speed changetransmission shaft externally inserted into the speed changeintermediate shaft in a relatively rotatable manner and coupled with thefirst element so as not to be relatively rotatable.

In this case, the input side first transmission mechanism has an inputside first driving gear relatively rotatably supported by a main drivingshaft operatively coupled with the driving source and an input sidefirst driven gear operatively coupled with the input side first drivinggear and made relatively unrotatable to the speed change transmissionshaft. The input side second transmission mechanism has an input sidesecond driving gear relatively rotatably supported by the main drivingshaft and an input side second driven gear operatively coupled with theinput side second driving gear and made relatively unrotatable to thesecond element. The output side first transmission mechanism has anoutput side first driving gear supported by the speed changeintermediate shaft so as not to be relatively rotatable and an outputside first driven gear operatively coupled with the output side firstdriving gear and relatively rotatably supported by the speed changeoutput shaft. The output side second transmission mechanism has anoutput side second driving gear supported by the speed changetransmission shaft so as not to be relatively rotatable and an outputside second driven gear operatively coupled with the output side seconddriving gear and relatively rotatably supported by the speed changeoutput shaft. The output side third transmission mechanism has an outputside third driving gear supported by the speed change transmission shaftso as not to be relatively rotatable and an output side third drivengear operatively coupled with the output third driving gear andrelatively rotatably supported by the speed change output shaft.

The transmission structure according to the present invention mayfurther include a traveling transmission shaft disposed on a downstreamside in a transmission direction relative to the speed change outputshaft, and a forward/reverse movement switching mechanism capable ofswitching a rotation direction of driving force in a forward movementdirection and a reverse movement direction between the speed changeoutput shaft and the traveling transmission shaft.

Also, in order to achieve the first object, a sixth aspect of thepresent invention provides a transmission mechanism including an HSTcontinuously changing rotation power operatively input into a pump shaftfrom a driving source to rotation power at least between first HST speedand second HST speed according to an operation position of an outputadjustment member, and then outputting the changed rotation power as anHST output from a motor shaft; a planetary gear mechanism having firstto third elements, in which the third element functions as an inputportion of the HST output; an input side first transmission mechanismcapable of operatively transmitting the rotation power of the drivingsource to the first element at an input side first speed change ratio;an input side second transmission mechanism capable of operativelytransmitting the rotation power of the driving source to the secondelement at an input side second speed change ratio; an input side firstand second clutch mechanisms engaging/disengaging power transmission ofthe input side first and second transmission mechanisms, respectively; aspeed change output shaft; a traveling transmission shaft disposed on adownstream side in a transmission direction relative to the speed changeoutput shaft; a forward/reverse movement switching mechanism interposedin a transmission path from the speed change output shaft to thetraveling transmission shaft and capable of switching the travelingtransmission state between a forward movement transmission state ofrotating the traveling transmission shaft in a forward movementdirection and a reverse movement transmission state of rotating thetraveling transmission shaft in a reverse movement direction; an outputside first transmission mechanism capable of operatively transmittingthe rotation power of the second element to the speed change outputshaft at an output side first speed change ratio; an output side secondtransmission mechanism capable of operatively transmitting the rotationpower of the first element to the speed change output shaft at an outputside second speed change ratio; an output side third transmissionmechanism which can operatively transmit the rotation power of the firstelement to the traveling transmission shaft as driving force in theforward movement direction and in which a speed change ratio is set sothat rotational speed of the traveling transmission shaft when therotation power of the first element is operatively transmitted to thetraveling transmission shaft through the output side third transmissionmechanism is higher than rotational speed of the traveling transmissionshaft when the rotation power of the first element is operativelytransmitted to the traveling transmission shaft through the output sidesecond transmission mechanism and the forward and reverse movementchange mechanism in the forward movement transmission state; output sidefirst to third clutch mechanisms engaging/disengaging power transmissionof the output side first to third transmission mechanisms, respectively;a speed change operation member; an HST sensor directly or indirectlydetecting a speed change state of the HST; and a control devicecontrolling operations of the output adjustment member, the input sidefirst and second clutch mechanisms, and the output side first to thirdclutch mechanisms.

The transmission structure according to the sixth aspect makes itpossible to expand the speed change range of the forward movement whichis high in frequency of use while effectively preventing or reducing therotational speed difference in the speed change output shaft inswitching between the first and second transmission states and betweenthe second and third transmission states.

In the sixth aspect,

the control device operates the output adjustment member so that the HSToutput is set to the first HST speed which makes a synthetic rotationpower of the planetary gear mechanism zero when the speed changeoperation member is positioned at a zero speed position,

when the speed change operation member is operated in a forward movementside low speed range from the zero speed position to a forward movementside first switching speed position, while the control device develops afirst transmission state where the first element is functioned as aninput portion of reference power operatively transmitted from thedriving source and the second element is functioned as an output portionof the synthetic rotation power by bringing the output side first clutchmechanism into an engagement state and bringing other output side clutchmechanisms into a disengagement state while bringing the input sidefirst clutch mechanism into the engagement state and bringing the inputside second clutch mechanism into the disengagement state, the controldevice brings the forward/reverse movement switching mechanism into theforward movement transmission state and the control device operates theoutput adjustment member so that the HST output is speed-changed fromthe side of the first HST speed toward the side of the second HST speedin response to an acceleration operation of the speed change operationmember,

when the speed change operation member is operated in a forward movementside intermediate speed range from the forward movement side firstswitching speed position to a forward movement side second switchingspeed position, while the control device develops a second transmissionstate where the second element is functioned as the input portion ofreference power and the rotation power of the first element isoperatively transmitted to the speed change output shaft at the outputside second speed change ratio by bringing the output side second clutchmechanism into the engagement state and bringing other output sideclutch mechanisms into the disengagement state while bringing the inputside first clutch mechanism into the disengagement state and bringingthe input side second clutch mechanism into the engagement state, thecontrol device brings the forward/reverse movement switching mechanisminto the forward movement transmission state and the control deviceoperates the output adjustment member so that the HST output isspeed-changed from the side of the second HST speed toward the side ofthe first HST speed in response to an acceleration operation of thespeed change operation member,

when the speed change operation member is operated in a forward movementside high speed range beyond the forward movement side second switchingspeed position, while the control device develops a third transmissionstate where the second element is functioned as the input portion ofreference power and the rotation power of the first element isoperatively transmitted to the traveling transmission shaft as drivingforce in the forward movement direction through the output side thirdtransmission mechanism by bringing the output side third clutchmechanism into the engagement state and bringing other output sideclutch mechanisms into the disengagement state while bringing the inputside first clutch mechanism into the disengagement state and bringingthe input side second clutch mechanism into the engagement state, thecontrol device operates the output adjustment member so that the HSToutput is speed-changed from the side of the second HST speed toward theside of the first HST speed in response to the acceleration operation ofthe speed change operation member,

when the speed change operation member passes the forward movement sidesecond switching speed position between the forward movement sideintermediate speed range and the forward movement side high speed range,the control device operates the output adjustment member so thatrotational speed of the traveling transmission shaft in a transmissionstate developed immediately after the passage coincides with orapproaches rotational speed of the traveling transmission shaft in atransmission state developed immediately before the passage,

when the speed change operation member is operated in a reverse movementside low speed range from the zero speed position to a reverse movementside first switching speed position, while the control device developsthe first transmission state, the control device brings theforward/reverse movement switching mechanism into the reverse movementtransmission state and operates the output adjustment member so that theHST output is speed-changed from the side of the first HST speed towardthe side of the second HST speed in response to the accelerationoperation of the speed change operation member, and

when the speed change operation member is operated in a reverse movementside high speed range beyond the reverse movement side first switchingspeed position, while the control device develops the secondtransmission state, the control device brings the forward/reversemovement switching mechanism into the reverse movement transmissionstate and operates the output adjustment member so that the HST outputis speed-changed from the side of the second HST speed toward the sideof the first HST speed in response to the acceleration operation of thespeed change operation member.

In the sixth aspect, the input side first and second speed change ratiosare set so that rotational speed of the second element when the HSToutput is set to the second HST speed in the first transmission stateand the rotational speed of the second element by rotation powertransmitted through the input side second transmission mechanism in thesecond transmission state are same and so that rotational speed of thefirst element when the HST output is set to the second HST speed in thesecond transmission state and the rotational speed of the first elementby rotation power transmitted through the input side first transmissionmechanism in the first transmission state are same.

The transmission structure according to the sixth aspect may include aspeed change intermediate shaft coupled with the second element so asnot to be relatively rotatable around an axis.

In this case, the input side first transmission mechanism has an inputside first driving gear relatively rotatably supported by a main drivingshaft operatively coupled with the driving source and an input sidefirst driven gear operatively coupled with the input side first drivinggear and the first element in a state of being relatively rotatablysupported by the speed change intermediate shaft. The input side secondtransmission mechanism has an input side second driving gear relativelyrotatably supported by the main driving shaft and an input side seconddriven gear operatively coupled with the input side second driving gearin a state of being supported by the speed change intermediate shaft soas not to be relatively rotatable. The output side first transmissionmechanism has an output side first driven gear operatively coupled withthe input side second driven gear in a state of relatively rotatablysupported by the speed change output shaft. The output side secondtransmission mechanism has an output side second driven gear operativelycoupled with the input side first driven gear in a state of beingrelatively rotatably supported by the speed change output shaft. Theoutput side third transmission mechanism has an output side third drivengear operatively coupled with one of the output side first and seconddriven gears in a state of being relatively rotatably supported by thetraveling transmission shaft.

The input side first and second clutch mechanisms are supported by themain driving shaft so as to engage/disengage the input side first andsecond driving gears, respectively, with/from the main driving shaft,the output side first and second clutch mechanisms are supported by thespeed change output shaft so as to engage/disengage the output sidefirst and second driven gears, respectively, with/from the speed changeoutput shaft, and the output side third clutch mechanism is supported bythe traveling transmission shaft so as to engage/disengage the outputside third driven gear with/from the traveling transmission shaft.

Preferably, the transmission structure according to the sixth aspect mayfurther include a hollow housing body; a first bearing plate detachablycoupled with the housing body; and a second bearing plate detachablycoupled with the housing body at a position spaced from the firstbearing plate in a longitudinal direction of the housing body.

In this case, the main driving shaft, the speed change intermediateshaft, the speed change output shaft, and the traveling transmissionshaft are supported by the first and second bearing plates in a state ofbeing parallel to one another. The input side first and second drivinggears and the input side first and second clutch mechanisms aresupported in a portion located in a partitioned space sandwiched betweenthe first and second bearing plates of the main driving shaft in a statewhere the input side first and second clutch mechanisms are locatedbetween the input side first and second driving gears with respect to anaxial direction of the main driving shaft. The the input side first andsecond driven gears are supported in a portion located in thepartitioned space of the speed change intermediate shaft in a state ofbeing located at same positions as positions of the input side first andsecond driving gears, respectively, with respect to the axial direction.The output side first and second driven gears and the output side firstand second clutch mechanisms are supported in a portion located in thepartitioned space of the speed change output shaft in a state where theoutput side first and second driven gears are located at same positionsas positions of the input side second and first driven gears,respectively, with respect to the axial direction and the output sidefirst and second clutch mechanisms are located between the input sidefirst and second driven gears with respect to the axial direction. Theoutput side third driven gear and the output side third clutch mechanismare supported in a portion located in the partitioned space of thetraveling transmission shaft in a state where the output side thirddriven gear is located at a same position in the axial direction as aposition of one of the output side first and second driven gears and theoutput side third clutch mechanism is located on a far side of one ofthe output side first and second driven gears from the output side firstand second clutch mechanisms with respect to the axial direction. Theforward/reverse movement switching mechanism is supported in a portionlocated outside the partitioned space of the speed change output shaftand the traveling transmission shaft.

In one example, the housing body has a front housing body and a rearhousing body detachably connected in series.

In this case, the first bearing plate is detachably coupled with a bossportion provided in an inner surface of the front housing body near arear opening of the front housing body, and the second bearing plate isdetachably coupled with a boss portion provided in an inner surface ofthe rear housing body near a front opening of the rear housing body.

In the fifth and sixth aspects, the output side first and second speedchange ratios may be set so that rotational speed developed in the speedchange output shaft when the HST output is set to the second HST speedis same in the first and second transmission states.

Alternatively, the control device may be configured to operate theoutput adjustment member so that, in switching between the first andsecond transmission states, rotational speed developed in the speedchange output shaft in a transmission state after the switchingcoincides with or approaches rotational speed developed in the speedchange output shaft in a transmission state before the switching.

In any one of the above configurations according to the presentinvention, assuming that a rotation direction of the rotation powerinput into the pump shaft is a normal rotation direction, the HSToutputs rotation power in one of normal and reverse directions as theHST output of the first HST speed and outputs rotation power in anotherone of the normal and reverse directions as the HST output of the secondHST speed.

In any one of the above configurations according to the presentinvention, an internal gear, a carrier, and a sun gear of the planetarygear mechanism form the first, second, and third elements, respectively.

In order to achieve the second object, the present invention provides aworking vehicle including a driving source; a driving wheel; and thetransmission structure according to any one of the above configurationsinterposed in the traveling system transmission path reaching thedriving wheel from the driving source, wherein switching speed of thespeed change output shaft is set to speed higher than speed in a workspeed range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transmission schematic view of a working vehicle to which atransmission structure according to an embodiment 1 of the presentinvention is applied.

FIG. 2 is a hydraulic circuit diagram of the transmission structureaccording to the embodiment 1.

FIGS. 3A and 3B are graphs illustrating the relationship between thetraveling vehicle speed and the rotational speed of the HST output inthe working vehicle to which the transmission structure according to theembodiment 1 is applied, and illustrate states where a sub speed changemechanism 240 provided in the transmission structure is engaged with alow speed stage and a high speed stage, respectively.

FIG. 4 is a hydraulic circuit diagram of a transmission structureaccording to an embodiment 2 of the present invention.

FIG. 5A and FIG. 5B illustrate graphs illustrating the relationshipbetween the traveling vehicle speed and the rotational speed of the HSToutput in a working vehicle to which the transmission structure 2 isapplied, and illustrate states where the sub speed change mechanism isengaged with a low speed stage and a high speed stage, respectively.

FIGS. 6A and 6B illustrate graphs illustrating the relationship betweenthe traveling vehicle speed and the rotational speed of the HST outputin a working vehicle to which a modification of the embodiment 2 isapplied, and illustrate states where the sub speed change mechanism isengaged with the low speed stage and the high speed stage, respectively.

FIG. 7 is a hydraulic circuit diagram of a transmission structure 3according to an embodiment 3 of the present invention.

FIG. 8 is hydraulic pressure waveform charts in switching from first tosecond transmission states in the transmission structure according theembodiment 3.

FIG. 9 is a hydraulic circuit diagram of a transmission structureaccording to an embodiment 4 of the present invention.

FIG. 10 is a partial cross sectional view of a vicinity of an input sideclutch unit of the transmission structure according to the embodiment 4,and shows a state in which an input side slider is positioned at a firstposition so that an input side first clutch mechanism is engaged and aninput side second clutch mechanism is disengaged.

FIG. 11 is a partial cross sectional view of the vicinity of the inputside clutch unit shown in FIG. 10 , and shows a state in which the inputside slider is positioned at an intermediate position so that both theinput side first and second clutch mechanism are engaged.

FIG. 12 is hydraulic pressure wave form charts in which the transmissionstructure according to the embodiment 4 is switched from a firsttransmission state to a second transmission states.

FIG. 13 is a hydraulic circuit diagram of a transmission structureaccording to a modification of the embodiments 3 or 4.

FIG. 14 is hydraulic pressure waveform charts in which the transmissionstructure according to the modification is switched from a firsttransmission state to a second transmission state.

FIG. 15 is hydraulic pressure waveform charts in which a transmissionstructure according to an embodiment 5 of the present invention isswitched from a first transmission state to a second transmission state.

FIG. 16 is a hydraulic circuit diagram of a transmission structureaccording to an embodiment 6 of the present invention.

FIG. 17 is hydraulic pressure waveform charts in which the transmissionstructure according to the embodiment 6 is switched from a firsttransmission state to a second transmission state.

FIG. 18 is hydraulic pressure waveform charts in which a transmissionstructure according to a modification of the embodiment 5 or 6 isswitched from a first transmission state to a second transmission state.

FIG. 19 is a transmission schematic view of a working vehicle to which atransmission structure according to an embodiment 7 of the presentinvention is applied.

FIG. 20 is a hydraulic circuit diagram of the transmission structureaccording to the embodiment 7.

FIGS. 21A and 21B are graphs illustrating the relationship between thetraveling vehicle speed and the HST output in the working vehicle towhich the transmission structure according to the embodiment 7 isapplied, and illustrate states where a sub speed change mechanismprovided in the transmission structure is engaged with a low speed stageand a high speed stage, respectively.

FIG. 22 is a hydraulic circuit diagram of a transmission structureaccording to a modification of the embodiment 7.

FIG. 23 is a transmission schematic view of a working vehicle to which atransmission structure according to an embodiment 8 of the presentinvention is applied.

FIG. 24 is a partial vertical cross-sectional side view of the workingvehicle shown in FIG. 23 .

FIG. 25 is a graph illustrating the relationship between the travelingvehicle speed and the HST output in the working vehicle shown in FIG. 23.

FIG. 26 is a transmission schematic view of a working vehicle to which atransmission structure according to a modification of the embodiment 8is applied.

FIG. 27 is a transmission schematic view of a working vehicle to which atransmission structure according to an embodiment 9 of the presentinvention is applied.

FIG. 28 is a partial vertical cross-sectional side view of the workingvehicle shown in FIG. 27 .

FIG. 29 is a graph illustrating the relationship between the travelingvehicle speed and the HST output in the working vehicle shown in FIG. 27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

Hereinafter, one embodiment of a transmission structure according to thepresent invention is described with reference to the accompanyingdrawings.

FIG. 1 illustrates a transmission schematic view of a working vehicle200 to which a transmission structure 1 according to this embodiment isapplied.

FIG. 2 illustrates a hydraulic circuit diagram of the transmissionstructure 1.

As illustrated in FIG. 1 and FIG. 2 , the working vehicle 200 isprovided with a driving source 210, driving wheels 220, and thetransmission structure 1 interposed in a traveling system transmissionpath reaching the driving wheels 220 from the driving source 210. Thereference numeral 210 a in FIG. 1 and FIG. 2 designates a flywheelcontained in the driving source 210.

As illustrated in FIG. 1 and FIG. 2 , the transmission structure 1 isprovided with a hydrostatic transmission (HST) 10, a planetary gearmechanism 30 forming an HMT structure (hydromechanical transmissionstructure) in cooperation with the HST 10, a speed change output shaft45, a speed change operation member 90, such as a speed change lever,capable of detecting the operation position by an operation positionsensor 92, an HST sensor 95 a directly or indirectly detecting the speedchange state of the HST 10, an output sensor 95 b directly or indirectlydetecting the rotational speed of the speed change output shaft 45, anda control device 100.

As illustrated in FIG. 1 and FIG. 2 , the HST 10 has a pump shaft 12operatively rotationally driven by the driving source 210, a hydraulicpump 14 supported by the pump shaft 12 so as not to be relativelyrotatable, a hydraulic motor 18 fluid-connected to the hydraulic pump 14through a pair of hydraulic oil lines 15 and hydraulically rotationallydriven by the hydraulic pump 14, a motor shaft 16 supporting thehydraulic motor 18 so as not to be relatively rotatable, and an outputadjustment member 20 varying the capacity of at least one of thehydraulic pump 14 and the hydraulic motor 18.

The HST 10 can continuously change the ratio of the rotational speed ofthe HST output to be output from the motor shaft 16 to the rotationalspeed of the power input into the pump shaft 12 (i.e., speed changeratio of the HST 10) according to the operation position of the outputadjustment member 20.

More specifically, when the rotational speed of the rotation poweroperatively input into the pump shaft 12 from the driving source 210 isset to a reference input speed, the HST 10 continuously changes therotation power of the reference input speed to the rotation power atleast between the first HST speed and the second HST speed according tothe operation position of the output adjustment member 20, and thenoutputs the changed rotation power from the motor shaft 16.

In this embodiment, the pump shaft 12 is coupled with a main drivingshaft 212 operatively coupled with the driving source 210 through a geartrain 214 as illustrated in FIG. 1 .

In this embodiment, the HST 10 is configured so that the rotationdirection of the HST output can be switched between the normal rotationdirection and the reverse rotation direction.

More specifically, the HST 10 is configured so that, in the case wherethe rotation direction of the reference input speed is set to the normalrotation direction, when the output adjustment member 20 is located at afirst operation position, the rotation power of the first HST speed inwhich the rotation direction is set to one of the normal rotationdirection and the reverse rotation direction (for example, reverserotation direction) is output from the motor shaft 16 and, when theoutput adjustment member 20 is located at a second operation position,the rotation power of the second HST speed in which the rotationdirection is set to the other one of the normal rotation direction andthe reverse rotation direction (for example, normal rotation direction)is output from the motor shaft 16.

In this case, when the output adjustment member 20 is located at aneutral position between the first and second operation positions, therotational speed of the HST output becomes neutral speed (zero speed).

In this embodiment, the HST 10 has, as the output adjustment member 20,a movable swash plate varying the capacity of the hydraulic pump 14 bybeing oscillated around an oscillation shaft and capable of beingoscillated to one side and the other side around the oscillation shaftacross the neutral position where the discharge amount of pressure oildischarged from the hydraulic pump 14 is set to zero as illustrated inFIG. 1 and FIG. 2 .

When the movable swash plate is located at the neutral position, thepressure oil is not discharged from the hydraulic pump 14, so that theHST 10 is brought into a neutral state where the output of the hydraulicmotor 18 is zero.

Then, when the movable swash plate is oscillated from the neutralposition to the normal rotation side which is the one side around theoscillation shaft, the pressure oil is supplied to one of the pair ofhydraulic oil lines 15 from the hydraulic pump 14, so that the onehydraulic oil line 15 becomes a high-pressure side and the otheroperation line 15 becomes a low-pressure side.

Thus, the hydraulic motor 18 is rotationally driven in the normalrotation direction, so that the HST 10 brought into a normal rotationoutput state.

On the contrary, when the movable swash plate is oscillated from theneutral position to the reverse rotation side which is the other sidearound the oscillation shaft, the pressure oil is supplied to the otherside of the pair of hydraulic oil lines 15 from the hydraulic pump 14,so that the other hydraulic oil line 15 becomes a high-pressure side andthe one hydraulic oil line 15 becomes a low-pressure side.

Thus, the hydraulic motor 18 is rotationally driven in the reverserotation direction, so that the HST 10 is brought into a reverserotation output state.

In the HST 10, the capacity of the hydraulic motor 18 is fixed by thefixed swash plate.

As illustrated in FIG. 2 , the output adjustment member 20 isoperatively controlled by the control device 100 based on the operationof the speed change operation member 90.

More specifically, the control device 100 operates the output adjustmentmember 20 through an actuator 110 based on the operation to the speedchange operation member 90.

The actuator 110 can take various configurations, such as an electricmotor and a hydraulic servo mechanism, insofar as the operation iscontrolled by the control device 100.

As illustrated in FIG. 1 and FIG. 2 , the planetary gear mechanism 30has a sun gear 32, a planetary gear 34 meshed with the sun gear 32, aninternal gear 36 meshed with the planetary gear 34, and a carrier 38supporting the planetary gear 34 so as to be rotatable around the axisand rotating around the axis of the sun gear 32 while interlocked withthe revolution around the sun gear 32 of the planetary gear 34, in whichthe sun gear 32, the carrier 38, and the internal gear 36 form threeplanetary elements.

A third element which is one of the three planetary elements isoperatively coupled with the motor shaft 16 and the third elementfunctions as a variable power input portion which inputs the HST output.

As illustrated in FIG. 1 and FIG. 2 , the sun gear 32 is set as thethird element in this embodiment.

In this embodiment, the sun gear 32 is operatively coupled with themotor shaft 16 through a gear train 216.

The transmission structure 1 according to this embodiment enablesswitching between a first transmission state where the first element isfunctioned as a reference power input portion inputting the referencerotation power from the driving source 210 and the second element isfunctioned as an output portion outputting synthetic rotation power, anda second transmission state where the first element is functioned as theoutput portion and the second element is functioned as the referencepower input portion.

Specifically, as illustrated in FIG. 1 and FIG. 2 , the transmissionstructure 1 has an input side first transmission mechanism 50(1) and aninput side second transmission mechanism 50(2) capable of operativelytransmitting the rotation power of the driving source 210 to the firstelement and the second element, respectively, an input side first clutchmechanism 60(1) and an input side second clutch mechanism 60(2)engaging/disengaging the power transmission of the input side firsttransmission mechanism 50(1) and the input side second transmissionmechanism 50(2), respectively, an output side first transmissionmechanism 70(1) and an output side second transmission mechanism 70(2)capable of operatively transmitting the rotation power of the firstelement and the second element, respectively, to the speed change outputshaft, and an output side first clutch mechanism 80(1) and an outputside second clutch mechanism 80(2) engaging/disengaging the powertransmission of the output side first transmission mechanism 70(1) andthe output side second transmission mechanism 70(2), respectively.

In this embodiment, the internal gear 36 and the carrier 38 function asthe first and second elements, respectively.

The input side first transmission mechanism 50(1) is configured to beable to transmit the rotation power of the driving source 210 to thefirst element (the internal gear 36 in this embodiment) at an input sidefirst speed change ratio.

In detail, as illustrated in FIG. 1 and FIG. 2 , the input side firsttransmission mechanism 50(1) has an input side first driving gear 52(1)relatively rotatably coupled with the main driving shaft 212 and aninput side first driven gear 54(1) meshed with the input side firstdriving gear 52(1) and coupled with the first element.

The input side second transmission mechanism 50(2) is configured to beable to transmit the rotation power of the driving source 210 to thesecond element (the carrier 38 in this embodiment) at an input sidesecond speed change ratio.

In detail, as illustrated in FIG. 1 and FIG. 2 , the input side secondtransmission mechanism 50(2) has an input side second driving gear 52(2)relatively rotatably supported by the main driving shaft 212 and aninput side second driven gear 54(2) meshed with the input side seconddriving gear 52(2) and coupled with the second element.

In this embodiment, the input side first and second clutch mechanisms60(1) and 60(2) are configured as friction plate clutch mechanisms.

In detail, the input side first clutch mechanism 60(1) has an input sideclutch housing 62 supported by the main driving shaft 212 so as not tobe relatively rotatable, an input side first friction plate group 64(1)containing a first driving side friction plate supported by the inputside clutch housing 62 so as not to be relatively rotatable and a firstdriven side friction plate supported by the input side first drivinggear 52(1) so as not to be relatively rotatable in a state of beingopposed to the first driving side friction plate, and an input sidefirst piston (not illustrated) causing the input side first frictionplate group 64(1) to be frictionally engaged.

The input side second clutch mechanism 60(2) has the input side clutchhousing 62, an input side second friction plate group 64(2) containing asecond driving side friction plate supported by the input side clutchhousing 62 so as not to be relatively rotatable and a second driven sidefriction plate supported by the input side second driving gear 52(2) soas not to be relatively rotatable in a state of being opposed to thesecond driving side friction plate, and an input side second piston (notillustrated) causing the input side second friction plate group 64(2) tobe frictionally engaged.

The output side first transmission mechanism 70(1) is configured to beable to transmit the rotation power of the second element to the speedchange output shaft 45 at an output side first speed change ratio.

In detail, the transmission structure has a speed change intermediateshaft 43 disposed coaxially with the planetary gear mechanism 30 andcoupled with one of the first and second elements so as not to berelatively rotatable around the axis.

In this embodiment, the speed change intermediate shaft 43 is coupledwith the second element so as not to be relatively rotatable.

Then, the output side first transmission mechanism 70(1) has an outputside first driving gear 72(1) supported by the speed change intermediateshaft 43 so as not to be relatively rotatable and an output side firstdriven gear 74(1) meshed with the output side first driving gear 72(1)and relatively rotatably supported by the speed change output shaft 45.

The output side second transmission mechanism 70(2) is configured to beable to transmit the rotation power of the first element to the speedchange output shaft 45 at an output side second speed change ratio.

In detail, the output side second transmission mechanism 70(2) has anoutput side second driving gear 72(2) coupled with the first element andan output side second driven gear 74(2) meshed with the output sidesecond driving gear 72(2) and relatively rotatably supported by thespeed change output shaft 45.

In this embodiment, the output side second driving gear 72(2) issupported by the speed change intermediate shaft 43 so as to berelatively rotatable.

In this embodiment, the output side first and second clutch mechanisms80(1) and 80(2) are configured as friction plate clutch mechanisms.

In detail, the output side first clutch mechanism 80(1) has an outputside clutch housing 82 supported by the speed change output shaft 45 soas not to be relatively rotatable, an output side first friction plategroup 84(1) containing a first driving side friction plate supported bythe output side first driven gear 74(1) so as not to be relativelyrotatable and a first driven side friction plate supported by the outputside clutch housing 82 so as not to be relatively rotatable in a stateof being opposed to the first driving side friction plate, and an outputside first piston (not illustrated) causing the output side firstfriction plate group to be frictionally engaged.

The output side second clutch mechanism 80(2) has the output side clutchhousing 82, an output side second friction plate group 84(2) containinga second driving side friction plate supported by the output side seconddriven gear 74(2) so as not to be relatively rotatable and a seconddriven side friction plate supported by the output side clutch housing82 so as not to be relatively rotatable in a state of being opposed tothe second driving side friction plate, and an output side second piston(not illustrated) causing the output side second friction plate group tobe frictionally engaged.

In the transmission structure 1 according to this embodiment, the inputside first and second clutch mechanisms 60(1) and 60(2) and the outputside first and second clutch mechanisms 80(1) and 80(2) are of ahydraulic type in which an engagement state is exhibited when itreceives pressure oil supply.

In detail, as illustrated in FIG. 2 , the transmission structure 1further has a pressure oil supply line 155, the upstream side of whichis fluid-connected to a hydraulic source 150, such as a hydraulic pump,a drain line 157, a first supply/discharge line 160(1)supplying/discharging pressure oil to the input side and output sidefirst clutch mechanisms 60(1) and 80(1), a second supply/discharge line160(2) supplying/discharging pressure oil to the input side and outputside second clutch mechanisms 60(2) and 80(2), and a switching valve165, the position of which is controlled by the control device 100.

The reference numeral 156 in FIG. 2 designates a relief valve settingthe hydraulic pressure of the pressure oil supply line 155.

The switching valve 165 is configured to be able to take a firstposition where the pressure oil supply/discharge line 155 isfluid-connected to the first supply/discharge line 160(1) and the secondsupply/discharge line 160(2) is fluid-connected to the drain line 157and a second position where the first supply/discharge line 160(1) isfluid-connected to the drain line 157 and the pressure oilsupply/discharge line 155 is fluid-connected to the secondsupply/discharge line 160(2).

As illustrated in FIG. 1 , the transmission structure 1 according tothis embodiment further has a traveling transmission shaft 235 disposedon the downstream side in the transmission direction relative to thespeed change output shaft 45 and a forward/reverse movement switchingmechanism 230 configured to be able to switch the rotation direction ofthe driving force between the forward movement direction and the reversemovement direction between the speed change output shaft 45 and thetraveling transmission shaft 235.

The forward/reverse movement switching mechanism 230 is configured sothat the forward movement direction and the reverse movement directionis switched by the control device 100 in response to the operation tothe forward movement side and the reverse movement side of the speedchange operation member 90, for example.

More specifically, when recognizing that the speed change operationmember 90 is operated to the forward movement side, the control device100 brings the forward/reverse movement switching mechanism 230 into aforward movement transmission state and, when recognizing that the speedchange operation member 90 is operated to the reverse movement side, thecontrol device 100 brings the forward/reverse movement switchingmechanism 230 into a reverse movement transmission state.

As illustrated in FIG. 1 , the transmission structure 1 according tothis embodiment is further provided with a second traveling transmissionshaft 245 disposed on the downstream side in the transmission directionrelative to the traveling transmission shaft 235 and a sub speed changemechanism 240 capable of changing, in multiple stages, the rotationalspeed of the driving force in two stages of a high speed stage and a lowspeed stage between the traveling transmission shaft 235 and the secondtraveling transmission shaft 245.

The sub speed change mechanism 240 is configured so that switchingbetween a high speed transmission state and a low speed transmissionstate is performed through a mechanical link mechanism or by the controldevice in response to a manual operation to a sub speed change operationmember (not illustrated), for example.

The working vehicle 200 has one pair of right and left main drivingwheels as the driving wheels 220. Therefore, the working vehicle 200further has a pair of main driving axles 250 correspondingly driving thepair of main driving wheels and a differential mechanism 260differentially transmitting the rotation power of the second travelingtransmission shaft 245 to the pair of main driving axles 250 asillustrated in FIG. 1 .

As illustrated in FIG. 1 , the working vehicle 200 further has atraveling brake mechanism 255 selectively applying braking force to themain driving axle 250, a differential lock mechanism 265 forciblysynchronously driving the pair of main driving axles 250 by the rotationpower from the second traveling transmission shaft 245, and a drivingforce take-out mechanism 270 for sub-driving wheels capable ofselectively outputting the rotation power branched from the secondtraveling transmission shaft 245 toward the sub-driving wheels.

Moreover, the working vehicle 200 has a PTO shaft 280 outputting therotation power to the outside and a PTO clutch mechanism 285 and a PTOmultistage speed change mechanism 290 interposed in a PTO transmissionpath reaching the PTO shaft 280 from the driving source 210.

Herein, the operation control of the HST 10, the input side first andsecond clutch mechanisms 60(1) and 60(2), and the output side first andsecond clutch mechanisms 80(1) and 80(2) by the control device 100 isdescribed.

FIG. 3A and FIG. 3B illustrate graphs illustrating the relationshipbetween the traveling vehicle speed and the rotational speed of the HSToutput in the working vehicle 200.

FIG. 3A and FIG. 3B illustrates states where the sub speed changemechanism 240 is engaged with a low speed stage and a high speed stage,respectively.

The control device 100 produces the first transmission state where thefirst element (the internal gear 36 in this embodiment) is functioned asthe reference power input portion which receives the reference poweroperatively transmitted from the driving source 210 and the secondelement (the carrier 38 in this embodiment) is functioned as an outputportion of the synthetic rotation power by bringing the input side andoutput side first clutch mechanisms 60(1) and 80(1) into an engagementstate and bringing the input side and output side second clutchmechanisms 60(2) and 80(2) into a disengagement state when the speedchange operation member 90 is operated before the switching speedpositions (i.e., in a low speed state where the rotational speed of thespeed change output shaft 45 is less than a predetermined switchingspeed based on a detection signal of the output sensor 95 b).

The output sensor 95 b may take various forms, such as a sensordetecting the rotational speed of the speed change output shaft 45 and asensor detecting the rotational speed of the driving wheel 20 or thedriving axle 250, insofar as the rotational speed of the speed changeoutput shaft 45 can be directly or indirectly recognized.

The low speed state where the rotational speed of the speed changeoutput shaft 45 is less than the predetermined switching speed meansthat, in a case where the traveling vehicle speed is set as a reference,the vehicle speed is within the range of −a(L) to +a (L) when the subspeed change mechanism 240 is engaged with the low speed stage (see FIG.3A) and the vehicle speed is within the range of −a(H) to +a (H) whenthe sub speed change mechanism 240 is engaged with the high speed stage(see FIG. 3B).

“+” and “−” of the traveling vehicle speed mean that the travelingdirections of the working vehicle 200 are the forward movement directionand the reverse movement direction, respectively.

In the first transmission state, the control device 100 operates theoutput adjustment member 20 so that the HST output is speed-changed fromthe first HST speed (reverse rotation side predetermined speed in thisembodiment) toward the second HST speed (normal rotation sidepredetermined speed in this embodiment) based on the HST sensor 95 a inresponse to an acceleration operation of the speed change operationmember 90.

The HST sensor 95 a may take various forms, such as a sensor detectingthe rotational speed of the motor shaft 16 and a sensor detecting theoperation position of the output adjustment member 20, insofar as theoutput state of the HST 10 can be detected.

More specifically, when the speed change operation member 90 is locatedbefore the switching speed position, the control device 100 produces thefirst transmission state, and then,

(1) when the speed change operation member 90 is located at a zero speedposition (vehicle stop position), the control device 100 locates theoutput adjustment member 20 at the first HST speed position (reverserotation side predetermined speed position in this embodiment) where theHST output is set to the first HST speed,

(2) until the speed change operation member 90 reaches the switchingspeed position (i.e., until the rotational speed of the speed changeoutput shaft 45 reaches the switching speed from the zero speed (in acase where the traveling vehicle speed in the working vehicle 200 ofthis embodiment is used as a reference, equivalent to the time until thetraveling vehicle speed reaches the vehicle speed −a(L) (in reversemovement) from the zero speed and the time until the traveling vehiclespeed reaches the vehicle speed +a(L) (in forward movement) from thezero speed when the sub speed change mechanisms 240 is in the low speedstage engagement state (FIG. 3A) and equivalent to the time until thetraveling vehicle speed reaches the vehicle speed −a(H) (in reversemovement) from the zero speed and the time until the traveling vehiclespeed reaches the vehicle speed +a(H) (in forward movement) from thezero speed when the sub speed change mechanism 240 is in the high speedstage engagement state (FIG. 3B)), the control device 100 operates theoutput adjustment member 20 so that the HST output is speed-changed fromthe side of the first HST speed to the side of the second HST speed inresponse to the acceleration operation of the speed change operationmember 90 (so that the output adjustment member 20 is moved from thereverse rotation side predetermined speed position side to a normalrotation side predetermined speed position side in this embodiment), and

(3) when the speed change operation member 90 is located at theswitching speed position (i.e., when the rotational speed of the speedchange output shaft 45 reaches the switching speed (in a case where thetraveling vehicle speed in the working vehicle 200 of this embodiment isused as a reference, equivalent to the time when the traveling vehiclespeed reaches the vehicle speed −a(L) (in reverse movement) and the timewhen the traveling vehicle speed reaches the vehicle speed +a(L) (inforward movement) when the sub speed change mechanisms 240 is in the lowspeed stage engagement state (FIG. 3A) and equivalent to the time whenthe traveling vehicle speed reaches the vehicle speed −a(H) (in reversemovement) and the time when the traveling vehicle speed reaches thevehicle speed +a(H) (in forward movement) when the sub speed changemechanism 240 is in the high speed stage engagement state (FIG. 3B)),the control device 100 operates the output adjustment member 20 at thesecond HST speed position (in this embodiment, normal rotation sidepredetermined speed position) where the HST output is set to the secondHST speed.

Furthermore, when recognizing that the speed change operation member 90is operated to the high speed side beyond the switching speed position(i.e., recognizing that the rotational speed of the speed change outputshaft 45 reaches a high speed state equal to or higher than thepredetermined switching speed based on a detection signal of the outputsensor 95 b), the control device 100 produces a second transmissionstate where the first element is functioned as an output portion and thesecond element is functioned as the reference power input portion bybringing the input side and output side first clutch mechanisms 60(1)and 80(1) into the disengagement state and bringing the input side andoutput side second clutch mechanisms 60(2) and 80(2) into the engagementstate.

The high speed state where the rotational speed of the speed changeoutput shaft 45 is equal to or higher than the predetermined switchingspeed means a state where, in a case where the traveling vehicle speedis used as a reference, the traveling vehicle speed is higher than orequal to −a(L) (in reverse movement) and higher than or equal to +a(L)(in forward movement) when the sub speed change mechanism 240 is engagedwith the low speed stage (see FIG. 3A) and, the traveling vehicle speedis higher than or equal to −a(H) (in reverse movement) and higher thanor equal to +a(H) (in forward movement) when the sub speed changemechanism 240 is engaged with the high speed stage (see FIG. 3B).

In the second transmission state, the control device 100 operates theoutput adjustment member 20 so that the HST output is speed-changed fromthe second HST speed (normal rotation side predetermined speed in thisembodiment) toward the first HST speed (the reverse rotation sidepredetermined speed in this embodiment) based on the HST sensor 95 a inresponse to the acceleration operation of the speed change operationmember 90.

More specifically, when the speed change operation member 90 is operatedto the forward movement high speed side relative to the switching speedposition, the control device 100 produces the second transmission state,and then,

(1) when the speed change operation member 90 is located at the speedswitching position, the control device 100 locates the output adjustmentmember 20 at the second HST speed position where the HST output is setto the second HST speed (normal rotation side predetermined speedposition in this embodiment),

(2) when the speed change operation member 90 is located between theswitching speed position and a forward movement maximum speed position(i.e., until the rotational speed of the speed change output shaft 45reaches the maximum speed from the switching speed (in a case where thetraveling vehicle speed in the working vehicle 200 of this embodiment isused as a reference, equivalent to the time until the traveling vehiclespeed reaches the vehicle speed −b(L) from the vehicle speed −a(L) (inreverse movement) and the time until the traveling vehicle speed reachesthe vehicle speed +b(L) from the vehicle speed +a(L) (in forwardmovement) when the sub speed change mechanism 240 is engaged with thelow speed stage (FIG. 3A) and equivalent to the time until the travelingvehicle speed reaches the vehicle speed −b(H) from the vehicle speed−a(H) (in reverse movement) and the time until the traveling vehiclespeed reaches the vehicle speed +b(H) from the vehicle speed +a(H) (inforward movement) when the sub speed change mechanism 240 is in the highspeed stage engagement state (FIG. 3B)), the control device 100 operatesthe output adjustment member 20 so that the HST output is speed-changedfrom the side of the second HST speed to the side of the first HST speedin response to the acceleration operation of the speed change operationmember 90 (the output adjustment member 20 is moved from the normalrotation side predetermined speed position to the reverse rotation sidepredetermined speed position in this embodiment), and

(3) when the speed change operation member 90 is operated to the forwardmovement maximum speed position (i.e., when the rotational speed of thespeed change output shaft 45 reaches the maximum speed (in a case wherethe traveling vehicle speed in the working vehicle 200 of thisembodiment is used as a reference, equivalent to the time when thetraveling vehicle speed reaches the vehicle speed −b(L) (in reversemovement) and the time when the traveling vehicle speed reaches thevehicle speed +b(L) (in forward movement) when the sub speed changemechanism 240 is in the low speed stage engagement state (FIG. 3A) andequivalent to the time when the traveling vehicle speed reaches thevehicle speed −b(H) (in reverse movement) and the time when thetraveling vehicle speed reaches the vehicle speed +b(H) (in forwardmovement) when the sub speed change mechanism 240 is in the high speedstage engagement state (FIG. 3B)), the control device 100 locates theoutput adjustment member 20 at the first HST speed position (the reverserotation side predetermined speed position in this embodiment) where theHST output is set to the first HST speed.

Herein, in this embodiment, the input side first and second speed changeratios are set so that the rotational speed of the second element is thesame in the interval of time between when the HST output is set to thesecond HST speed under the first transmission state where the secondelement functions as the output portion and when the second transmissionstate is realized where the second element functions as the referencepower input portion that receives the reference power from the drivingsource 210 operatively transmitted through the input side secondtransmission mechanism 50(2). The input side first and second speedratios are also set so that the rotational speed of the first element isthe same in the interval of time between when the HST output is set tothe second HST speed under the second transmission state where the firstelement functions as the output portion and when the first transmissionstate is realized where the first element functions as the referencepower input portion that receives the reference power from the drivingsource operatively transmitted through the input side first transmissionmechanism 50(1).

More specifically, in this embodiment, the input side first and secondspeed change ratios are set so that a rotational speed difference doesnot occur in the second element and the third element during thetransition between the first transmission state (where the first elementis functioned as the reference power input portion and the secondelement is functioned as the output portion) and the second transmissionstate (where the first element is functioned as the output portion andthe second element is functioned as the reference power input portion).

Furthermore, in this embodiment, the output side first and second speedchange ratios are set so that the rotational speed developed in thespeed change output shaft 45 when the HST output is set to the secondHST speed is same in the first and second transmission states.

More specifically, in this embodiment, the output side first and secondspeed change ratios are set so that a change does not occur in therotational speed of the speed change output shaft 45, i.e., thetraveling vehicle speed, during the transition between the first andsecond transmission states.

According to the transmission structure 1 provided with such aconfiguration, as illustrated in FIG. 3 , a continuous speed change canbe achieved over the speed change range where the speed change outputshaft 45 is accelerated by speed-changing the HST output from the firstHST speed to the second HST speed (speed change range of 0 to −a and 0to +a in a case where the traveling vehicle speed is used as areference, which is hereinafter referred to as a low speed side speedchange range) and the speed change range where the speed change outputshaft 45 is accelerated by speed-changing the HST output from the secondHST speed to the first HST speed (speed change range of −a to −b and +ato +b in a case where the traveling vehicle speed is used as areference, which is hereinafter referred to as a high speed side speedchange range).

Furthermore, in the switching between the low speed side speed changerange (first transmission state) and the high speed side speed changerange (second transmission state), a change in the operation position ofthe output adjustment member 20 of the HST 10 is not required and achange in the traveling vehicle speed is not caused.

Therefore, the switching can be smoothly performed without applying aload to constituent members of the traveling system transmission path inwhich the transmission structure 1 is interposed.

Moreover, the transmission structure 1 enables the switching withoutcausing a speed difference between the low speed side speed change range(first transmission state) and the high speed side speed change range(second transmission state) without being provided with two or more theplanetary gear mechanisms 30, and thus enables the realization of goodtransmission efficiency.

More specifically, when two or more of the planetary gear mechanisms areprovided, the switch between the transmission state in the low speedside speed change range and the transmission state in the high speedside speed change range is enabled without requiring a change in theoperation position of the output adjustment member of the HST andwithout causing a traveling vehicle speed change.

However, the transmission efficiency of the planetary gear mechanism ispoor, and thus good transmission efficiency cannot be obtained in theconfiguration provided with two or more of the planetary gearmechanisms.

In contrast thereto, the transmission structure 1 can obtain theabove-described effect by simply being provided with the singleplanetary gear mechanism 30.

Moreover, in the transmission structure 1 according to this embodiment,the input side first and second clutch mechanisms 60(1) and 60(2) andthe output side first and second clutch mechanisms 80(1) and 80(2) areconfigured as the friction plate clutch mechanisms as described above.

According to such a configuration, the switching between the low speedside speed change range (first transmission state) and the high speedside speed change range (second transmission state) can be more smoothlyperformed.

Preferably, the switching speed of the speed change output shaft 45serving as the target speed to start the switch between the first andsecond transmission states can be set to a speed higher than speed inthe work speed range set in the working vehicle 200.

More specifically, working vehicles, such as a tractor and a combine,perform heavy load work, such as tilling work, plowing work, tampingwork, and reaping work, while traveling at low speed in many cases.

In general, in the working vehicles, the traveling vehicle speed inperforming such heavy load work is set as the work speed range.Traveling vehicle speed of 0 to 8 km/h is usually set as the work speedrange and, depending on the specification, traveling vehicle speed of 0to 10 km/h is set as the work speed range.

Therefore, by setting the switching speed of the speed change outputshaft 45 to be higher than the speed in the work speed range in a casewhere the traveling vehicle speed is used as a reference, it can beeffectively prevented that the switching between the first and secondtransmission states is performed in the state where the heavy load workis performed.

Embodiment 2

Hereinafter, another embodiment of the transmission structure accordingto the present invention is described with reference to the accompanyingdrawings.

FIG. 4 illustrates a hydraulic circuit diagram of a transmissionstructure 2 according to this embodiment.

In the figure, the same components as those in Embodiment 1 describedabove are designated by the same reference numerals and a descriptionthereof is omitted as appropriate.

The transmission structure 2 according to this embodiment is differentfrom the transmission structure 1 according to Embodiment 1 in a pointthat the output side first and second transmission mechanisms 70(1) and70(2) are deleted.

In this embodiment, the output side first and second clutch mechanisms80(1) and 80(2) are provided to engage/disengage the power transmissionfrom the second element (the carrier 38 in this embodiment) and thefirst element (the internal gear 36 in this embodiment), respectively,to the speed change output shaft 45.

FIG. 5A and FIG. 5B illustrate graphs illustrating the relationshipbetween the traveling vehicle speed and the rotational speed of the HSToutput in a working vehicle to which the transmission structure 2 isapplied.

FIG. 5A and FIG. 5B illustrate states where the sub speed changemechanism 240 is engaged with a low speed stage and a high speed stage,respectively.

As illustrated in FIG. 5A and FIG. 5B, in this embodiment, the controldevice 100 is configured to perform switching from the firsttransmission state to the second transmission state when the speedchange operation member 90 is operated from the zero speed position tothe first switching speed positions, i.e., when recognizing that thespeed change output shaft 45 reaches a predetermined first switchingspeed in the first transmission state based on a detection signal of theoutput sensor 95 b (in a case where the traveling vehicle speed is usedas a reference, −a(L)(1) (in reverse movement) or +a(L)(1) (in forwardmovement) in the low speed stage engagement and −a(H)(1) (in reversemovement) or +a(H)(1) (in forward movement) in the high speed stageengagement).

Herein, when the HST output is set to the second HST speed in the firsttransmission state, the rotational speed of the first switching speed isdeveloped in the speed change output shaft 45.

More specifically, when the reference power from the driving source 210is operatively input into the first element (the internal gear 36 inthis embodiment), the HST output of the second HST speed is operativelyinput into the third element (the sun gear 32 in this embodiment), andthe synthetic rotation power is output from the second element (thecarrier 38 in this embodiment), the speed change output shaft 45 rotatesat the first switching speed by the synthetic rotation power operativelytransmitted from the second element.

At this time, the traveling vehicle speed is set to −a(L)(1) (in reversemovement) or +a(L)(1) (in forward movement) (FIG. 5A) in the low speedstage engagement of the sub speed change mechanism 240 and is set to−a(H)(1) (in reverse movement) or +a(H)(1) (in forward movement) (FIG.5B) in the high speed stage engagement of the sub speed change mechanism240.

When the speed change operation member 90 is operated to the firstswitching speed positions (i.e., when the switching from the firsttransmission state to the second transmission state is performed due tothe fact that the HST output is set to the second HST speed, so that therotational speed of the speed change output shaft 45 reaches the firstswitching speed in the first transmission state), a state is set wherethe reference power from the driving source 210 is operatively inputinto the second element (the carrier 38 in this embodiment), the HSToutput of the second HST speed is operatively input into the thirdelement (the sun gear 32 in this embodiment), and the synthetic rotationpower is output from the first element (the internal gear 38 in thisembodiment), so that the speed change output shaft 45 is rotated by thesynthetic rotation power operatively transmitted from the first element.

At this time, the transmission structure 2 according to this embodimentdoes not have the output side first and second transmission mechanisms70(1) and 70(2) as described above, and therefore the rotational speedof the speed change output shaft 45 changes from the first switchingspeed to a second switching speed.

The traveling vehicle speed when the rotational speed of the speedchange output shaft 45 is the second switching speed becomes −a(L)(2)(in reverse movement) or +a(L)(2) (in forward movement) (FIG. 5A) in thelow speed stage engagement of the sub speed change mechanism 240, andbecomes −a(H)(2) (in reverse movement) or +a(H)(2) (in forward movement)(FIG. 5B) in the high speed stage engagement of the sub speed changemechanism 240.

More specifically, in the transmission structure 2 according to thisembodiment, a rotational speed difference occurs in the speed changeoutput shaft 45 in the switching between the first and secondtransmission states, so that the traveling vehicle speed changes.

However, the rotational speed difference is not so large, and thereforecan be absorbed by components forming the traveling system transmissionpath.

In particular, in this embodiment, the input side first and secondclutch mechanisms 60(1) and 60(2) and the output side first and secondclutch mechanisms 80(1) and 80(2) are configured as the friction plateclutch mechanisms, and thus the rotational speed difference can beeffectively absorbed by the friction plate clutch mechanisms.

In place thereof, the input side second clutch mechanism 60(2) broughtinto the engagement state in the second transmission state out of theinput side first and second clutch mechanisms 60(1) and 60(2) and theoutput side second clutch mechanism 80(2) brought into the engagementstate in the second transmission state out of the output side first andsecond clutch mechanisms 80(1) and 80(2) can be configured as thefriction plate clutch mechanisms and the remaining clutch mechanisms60(1) and 80(1) can be configured as the other forms, such as a dogclutch mechanism.

According to the transmission structure 2 having such a configuration,although a certain traveling speed difference occurs in the switchingbetween the first and second transmission states, the structure can besimplified by the deletion of the output side first and secondtransmission mechanisms 70(1) and 70(2) as compared with Embodiment 1.

FIG. 6A and FIG. 6B illustrate graphs illustrating the relationshipbetween the traveling vehicle speed and the rotational speed of the HSToutput in a modification of this embodiment.

FIG. 6A and FIG. 6B illustrate states where the sub speed changemechanism 240 is engaged with the low speed stage and the high speedstage, respectively.

In the modification, the control device 100 operates the outputadjustment member 20 so that the switching speed in a transmission stateafter the switching coincides with or approaches the switching speed ina transmission state before the switching in the switching between thefirst and second transmission states.

More specifically, in a case where the switching from the firsttransmission state to the second transmission state is taken as anexample, the control device 100 is configured to operate the outputadjustment member 20 so that the switching speed (second switchingspeed) in the second transmission state which is a transmission stateafter the switching coincides with or approaches the switching speed(first switching speed) in the first transmission state which is thetransmission state before the switching.

Such a modification can effectively prevent or reduce the occurrence ofthe rotational speed difference in the speed change output shaft 45 inthe switching between the first and second transmission states, i.e. theoccurrence of a traveling speed difference.

Embodiment 3

Hereinafter, a still another embodiment of the transmission structureaccording to the present invention is described with reference to theaccompanying drawings.

FIG. 7 illustrates a hydraulic circuit diagram of a transmissionstructure 3 according to this embodiment.

In the figure, the same components as those in Embodiments 1 and 2described above are designated by the same reference numerals and adescription thereof is omitted as appropriate.

The transmission structure 3 according to this embodiment is differentfrom the transmission structure 1 according to Embodiment 1 in a pointthat a double transmission state where both the input side first andsecond clutch mechanisms 60(1) and 60(2) are brought into the engagementstate and both the output side first and second clutch mechanisms 80(1)and 80(2) are brought into the engagement state is developed in theswitching transition stage of the first and second transmission states.

Specifically, the transmission structure 3 is different from thetransmission 1 according to Embodiment 1 in the pressure oilsupply/discharge configuration to the input side first and second clutchmechanisms 60(1) and 60(2) and the output side first and second clutchmechanisms 80(1) and 80(2).

More specifically, as illustrated in FIG. 7 , the transmission structure3 is provided with the pressure oil supply line 155, an input side firstsupply/discharge line 360(1), an input side second supply/discharge line360(2), an output side first supply/discharge line 362(1) and an outputside second supply/discharge line 362(2) supplying/discharging pressureoil to the input side first clutch mechanism 60(1), the input sidesecond clutch mechanism 60(2), the output side first clutch mechanism80(1) and the output side second clutch mechanism 80(2), respectively,an input side first electromagnetic valve 365(1), an input side secondelectromagnetic valve 365(2), an output side first electromagnetic valve367(1) and an output side second electromagnetic valve 367(2) interposedbetween the pressure oil supply line 155 and the input side firstsupply/discharge line 360(1), the input side second supply/dischargeline 360(2), the output side first supply/discharge line 362(1) and theoutput side second supply/discharge line 362(2), respectively, and aninput side first pressure sensor 370(1), an input side second pressuresensor 370(2), an output side first pressure sensor 372(1) and an outputside second pressure sensor 372(2) interposed in the input side firstsupply/discharge line 360(1), the input side second supply/dischargeline 360(2), the output side first supply/discharge line 362(1) and theoutput side second supply/discharge line 362(2), respectively.

Each of the electromagnetic valves 365(1), 365(2), 367(1) and 367(2) isconfigured to be able to take a discharge position where thecorresponding supply/discharge line 360(1), 360(2), 362(1) and 362(2) isdrained and a supply position where the corresponding supply/dischargeline 360(1), 360(2), 362(1) and 362(2) is fluid-connected to thepressure oil supply line 155.

In this embodiment, each of the electromagnetic valves 365(1), 365(2),367(1) and 367(2) is biased toward the discharge positions by a biasingmember and located at the supply position against the pressing force ofthe biasing member when a control signal from the control device 100 isinput.

In this embodiment, as illustrated in FIG. 7 , each of theelectromagnetic valve 365(1), 365(2), 367(1) and 367(2) is configured asa proportional electromagnetic valve that receives the hydraulicpressure of the corresponding supply/discharge line 360(1), 360(2),362(1) and 362(2) as pilot pressure to thereby maintain the hydraulicpressure of the corresponding supply/discharge line 360(1), 360(2),362(1) and 362(2) at engagement hydraulic pressure in a state where aposition signal to the supply position is input from the control device100.

The position control of the electromagnetic valves 365(1), 365(2),367(1) and 367(2) by the control device 100 is described taking a caseof the switching from the first transmission state to the secondtransmission state as an example.

FIG. 8 illustrates hydraulic pressure waveform charts of thesupply/discharge lines 360(1), 360(2), 362(1) and 362(2) in theswitching from the first transmission state to the second transmissionstate.

In a state where the speed change operation member 90 is located betweenthe zero speed position and the switching speed position (i.e., in a lowspeed state where the rotational speed of the speed change output shaft45 is less than the switching speed), the control device 100 locates theinput side first electromagnetic valve 365(1) and the output side firstelectromagnetic valve 367(1) at the supply positions and locates theinput side second electromagnetic valve 365(2) and the output sidesecond electromagnetic valve 367(2) at the discharge positions.

In this state, while the hydraulic pressure of the input side secondsupply/discharge line 360(2) and the output side second supply/dischargeline 362(2) are released, so that the input side second clutch mechanism60(2) and the output side second clutch mechanism 80(2) are brought intothe disengagement state, the input side first supply/discharge line360(1) and the output side first supply/discharge line 362(1) aremaintained at the engagement hydraulic pressure set by the pilotpressure of the corresponding electromagnetic valves 365(1) and 367(1),so that the input side first clutch mechanism 60(1) and the output sidefirst clutch mechanism 80(1) are brought into the engagement state.

Thus, the transmission structure 3 is brought into the firsttransmission state.

Meanwhile, in a state where the speed change operation member 90 isoperated beyond the switching speed position (i.e., in a high speedstate where the rotational speed of the speed change output shaft 45 isequal to or higher than the switching speed), the control device 100locates the input side first electromagnetic valve 365(1) and the outputside first electromagnetic valve 367(1) at the discharge positions andlocates the input side second electromagnetic valve 365(2) and theoutput side second electromagnetic valve 367(2) at the supply positions.

In this state, while the hydraulic pressure of the input side firstsupply/discharge line 360(1) and the output side first supply/dischargeline 362(1) is released, so that the input side first clutch mechanism60(1) and the output side first clutch mechanism 80(1) are brought intothe disengagement state, the input side second supply/discharge line360(2) and the output side second supply/discharge line 362(2) aremaintained at the engagement hydraulic pressure set by the pilotpressure of the corresponding electromagnetic valves 365(2) and 367(2),so that the input side second clutch mechanism 60(2) and the output sidesecond clutch mechanism 80(2) are brought into the engagement state.

Thus, the transmission structure 3 is brought into the secondtransmission state.

Herein, when recognizing that the speed change operation member 90 isoperated to the switching speed position at time Ta (see FIG. 8 ),(i.e., when recognizing that the rotational speed of the speed changeoutput shaft 45 reaches the switching speed from the state where therotational speed is less than the switching speed based on a signal fromthe output sensor 95 b), the control device 100 moves the input sidesecond electromagnetic valve 365(2) and the output side secondelectromagnetic valve 367(2) located at the discharge positions at thetime before the switching to the supply positions from the dischargepositions while maintaining the input side first electromagnetic valve365(1) and the output side first electromagnetic valve 367(1) located atthe supply positions at the time before the switching of thetransmission state (at the time of the first transmission state in thisexample) at the supply positions.

Thus, while the input side first supply/discharge line 360(1) and theoutput side first supply/discharge line 362(1) are maintained at theengagement hydraulic pressure, the hydraulic pressure of the input sidesecond supply/discharge line 360(2) and the output side secondsupply/discharge line 362(2) increase to the engagement hydraulicpressure at time Tb, so that the double transmission state is developed.

Thereafter, the control device 100 moves the input side firstelectromagnetic valve 365(1) and the output side first electromagneticvalve 367(1) located at the supply positions at the time before theswitching from the supply positions to the discharge positions whenpredetermined time (time Tc) has passed from the time (time Tb) whenrecognizing that the hydraulic pressure of the input side secondsupply/discharge line 360(2) and the output side second supply/dischargeline 362(2) to which pressure oil is supplied through the input sidesecond electromagnetic valve 365(2) and the output side secondelectromagnetic valve 367(2) moved to the supply positions reaches theengagement hydraulic pressure based on the signals from thecorresponding pressure sensors 370(2) and 372(2).

Thus, the second transmission state where, while the input side secondclutch mechanism 60(2) and the output side second clutch mechanism 80(2)are brought into the engagement state, the input side first clutchmechanism 60(1) and the output side first clutch mechanism 80(1) arebrought into the disengagement state is developed.

The transmission structure 3 according to this embodiment having such aconfiguration can effectively prevent the occurrence of a state wheretraveling driving force is not transmitted to the driving wheels 220 inthe switching between the first and second transmission states.

This is particularly effective when the switching between the first andsecond transmission states occurs in the work traveling.

This embodiment is configured so that the engagement states of thecorresponding friction plate clutch mechanisms are detected based on thepressure sensors 370(1), 370(2), 372(1) and 372(2). However, in place ofthe configuration, this embodiment can be configured so that theengagement states of the corresponding friction plate clutch mechanismsare detected based on other clutch engagement detection units detectinga supply current value, supply current time, and the like of theproportional electromagnetic valves 365(1), 365(2), 367(1) and 367(2).

Embodiment 4

Hereinafter, yet still another embodiment of the transmission structureaccording to the present invention is described with reference to theaccompanying drawings.

FIG. 9 illustrates a hydraulic circuit diagram of a transmissionstructure 4 according to this embodiment.

In the figure, the same components as those in Embodiments 1 to 3described above are designated by the same reference numerals and adescription thereof is omitted as appropriate.

The transmission structure 4 according to this embodiment has an inputside clutch unit 410 and an output side clutch unit 430 of a dog clutchtype in place of the input side first and second clutch mechanisms 60(1)and 60(2) and the output side first and second clutch mechanisms 80(1)and 80(2) of the friction plate type as compared with the transmissionstructure 1 according to Embodiment 1.

FIG. 10 illustrates a partial cross sectional view of the input sideclutch unit 410.

As illustrated in FIG. 10 , the input side clutch unit 410 has an inputside slider 412 supported by a corresponding main driving shaft 212 soas not to be relatively rotatable and so as to be movable in the axialdirection.

The input side slider 412 is disposed between the input side first andsecond driving gears 52(1) and 52(2) and has a first recess-projectionengagement portion 412(2) on one side in the axial direction close tothe input side first driving gear 52(1) and a second recess-projectionengagement portion 412(1) on the other side in the axial direction closeto the input side second driving gear 52(2).

The input side clutch unit 410 further has recess-projection engagementportions 414(1) and 414(2) formed in the input side first and seconddriving gears 52(1) and 52(2), respectively.

More specifically, when the input side slider 412 is located at a firstposition on the one side in the axial direction illustrated in FIG. 10 ,while the second recess-projection engagement portion 412(2) is notengaged with the recess-projection engagement portion 414(2) of theinput side second driving gear 52(2), the first recess-projectionengagement portion 412(1) is engaged with the recess-projectionengagement portion 414(1) of the input side first driving gear 52(1),whereby the input side first driving gear 52(1) is coupled with the maindriving shaft 212, so that the input side slider 412 brings only aninput side first clutch mechanism formed by the first recess-projectionengagement portion 412(1) and the recess-projection engagement portion414(1) into the engagement state.

When the input side slider 412 is located at a second position on theother side in the axial direction, while the first recess-projectionengagement portion 412(1) is not engaged with the recess-projectionengagement portion 414(1) of the input side first driving gear 52(1),the second recess-projection engagement portion 412(2) is engaged withthe recess-projection engagement portion 414(2) of the input side seconddriving gear 52(2), whereby the input side second driving gear 52(2) iscoupled with the main driving shaft 212, so that the input side slider412 brings only the input side second clutch mechanism formed by thesecond recess-projection engagement portion 412(2) and therecess-projection engagement portion 414(2) into the engagement state.

As illustrated in FIG. 11 , when the input side slider 412 is located atan intermediate position between the first and second positions withrespect to the axial direction, the first and second recess-projectionengagement portions 412(1) and 412(2) are engaged with therecess-projection engagement portions 414(1) and 414(2) of the inputside first and second driving gears 52(1) and 52(2), respectively,whereby the input side slider 412 brings both the input side first andsecond driving gears 52(1) and 52(2) are coupled with the main drivingshaft 212, so that both the input side first and second clutchmechanisms into the engagement state.

More specifically, when the input side slider 412 moves between thefirst position where the first transmission state is developed and thesecond position where the second transmission state is developed, theinput side slider 412 certainly passes the intermediate position whereboth the input side first and second clutch mechanisms are brought intothe engagement state.

The transmission structure 4 according to this embodiment having such aconfiguration can also effectively prevent the generation of the statewhere the traveling driving force is not transmitted to the drivingwheels in the switching between the first and second transmissionstates.

The output side clutch unit 430 has substantially the same configurationas that of the input side clutch unit 410.

More specifically, the output side clutch unit 430 has arecess-projection engagement portion (not illustrated) formed in each ofthe output side first and second driven gears 74(1) and 74(2) and anoutput side slider 432 supported by the corresponding speed changeoutput shaft 45 so as not to be relatively rotatable and so as to bemovable in the axial direction between the output side first and seconddriven gears 74(1) and 74(2) with respect to the axial direction.

The output side slider 432 has a first recess-projection engagementportion (not illustrated) on one side in the axial direction close tothe output side first driven gear 74(1) and a second recess-projectionengagement portion (not illustrated) on the other side in the axialdirection close to the output side second driven gear 74(2).

When the output side slider 432 is located at the first position on theone side in the axial direction, while the second recess-projectionengagement portion is not engaged with a recess-projection engagementportion of the output side second driven gear 74(2), the firstrecess-projection engagement portion is engaged with a recess-projectionengagement portion of the output side first driven gear 74(1), wherebythe output side first driven gear 74(1) is coupled with the speed changeoutput shaft 45, so that the output side slider 432 brings only anoutput side first clutch mechanism formed by the first recess-projectionengagement portion and the recess-projection engagement portion of theoutput side first driven gear 74(1) into the engagement state.

When the output side slider 432 is located at the second position on theother side in the axial direction, while the first recess-projectionengagement portion is not engaged with the recess-projection engagementportion of the output side first driven gear 74(1), the secondrecess-projection engagement portion is engaged with therecess-projection engagement portion of the output side second drivengear 74(2), whereby the output side second driven gear 74(2) is coupledwith the speed change output shaft 45, so that the output side slider432 brings only an output side second clutch mechanism formed by thesecond recess-projection engagement portion and the recess-projectionengagement portion of the output side second driven gear 74(2) into theengagement state.

Furthermore, when the output side slider 432 is located at anintermediate position between the first and second positions withrespect to the axial direction, the first and second recess-projectionengagement portions are engaged with the recess-projection engagementportions of the output side first and second driven gears 74(1) and74(2), respectively, whereby both the output side first and seconddriven gears 74(1) and 74(2) are coupled with the speed change outputshaft 45, so that the input side slider 432 brings both the output sidefirst and second clutch mechanisms into the engagement state.

The transmission structure 4 according to this embodiment has ahydraulic driving mechanism as a pressing mechanism for the input sideslider 412 and the output side slider 432.

The hydraulic driving mechanism is provided with the pressure oil supplyline 155, the drain line 157, an input side first oil chamber 450(1)pressing the input side slider 412 toward the first position by pressureoil to be supplied, an input side second oil chamber 450(2) pressing theinput side slider 412 toward the second position by pressure oil to besupplied, an output side first oil chamber 452(1) pressing the outputside slider 432 toward the first position by pressure oil to besupplied, an output side second oil chamber 452(2) pressing the outputside slider 432 toward the second position by pressure oil to besupplied, a first supply/discharge line 460(1) supplying/dischargingpressure oil to the input side first oil chamber 450(1) and the outputside first oil chamber 452(1), a second supply/discharge line 460(2)supplying/discharging pressure oil to the input side second oil chamber450(2) and the output side second oil chamber 452(2), and anelectromagnetic valve 465, the position of which is control by thecontrol device 100.

In the figure, the reference numeral 414 designates a biasing memberpressing the input side slider 412 toward one side in the axialdirection (first position in the example illustrated in the figure) andthe reference numeral 434 designates a biasing member pressing theoutput side slider 432 toward one side in the axial direction (firstposition in the example illustrated in the figure).

The electromagnetic valve 465 is configured to be able to take a firstposition where the pressure oil supply/discharge line 155 isfluid-connected to the first supply/discharge line 460(1) and the secondsupply/discharge line 460(2) is fluid-connected to the drain line 157and a second position where the first supply/discharge line 460(1) isfluid-connected to the drain line 157 and the pressure oilsupply/discharge line 155 is fluid-connected to the secondsupply/discharge line 460(2).

FIG. 12 illustrates hydraulic pressure wave form charts of the first andsecond supply/discharge lines 460(1) and 460(2) in the switching fromthe first transmission state to the second transmission state.

The control device 100 locates the electromagnetic valve 465 at thefirst position in a state where the speed change operation member 90 islocated between the zero speed position and the switching speed position(i.e., in a low speed state where the rotational speed of the speedchange output shaft 45 is less than the switching speed).

In this state, the hydraulic pressure of the second supply/dischargeline 460(2) is released and pressure oil is supplied to the firstsupply/discharge line 460(1), and thereby the input side slider 412 andthe output side slider 432 are located at the first position.

Thus, while the input side second clutch mechanism and the output sidesecond clutch mechanism are brought into the disengagement state, theinput side first clutch mechanism and the output side first clutchmechanism are brought into the engagement state, so that thetransmission structure 4 is brought into the first transmission state.

In a state where the speed change operation member 90 exceeds theswitching speed position (in the high speed state where the rotationalspeed of the speed change output shaft 45 is equal to or higher than theswitching speed), the control device 100 locates the electromagneticvalve 465 at the second position.

In this state, the hydraulic of the first supply/discharge line 460(1)is released and pressure oil is supplied to the second supply/dischargeline 460(2), and thereby the input side slider 412 and the output sideslider 432 are located at the second position.

Thus, while the input side first clutch mechanism and the output sidefirst clutch mechanism are brought into the disengagement state, theinput side second clutch mechanism and the output side second clutchmechanism are brought into the engagement state, so that thetransmission structure is brought into the second transmission state.

Herein, when recognizing that the speed change operation member 90 isoperated from the zero speed position side to the switching speedposition at time Ta (see FIG. 12 ) (i.e., when recognizing that therotational speed of the speed change output shaft 45 reaches theswitching speed from the state where the rotational speed is less thanthe switching speed based on a signal from the output sensor 95 b), thecontrol device 100 moves the electromagnetic valve 465 from the firstposition to the second position.

Thus, the input side slider 412 and the output side slider 432 are movedtoward the second position from the first position where the input sideslider 412 and the output side slider 432 are located at the time Ta,and then reach the second position at the time Tb. Then, the doubletransmission state is developed at the intermediate position in themiddle of the movement.

Although both the input side clutch unit and the output side clutch unitare configured as the friction plate type in Embodiment 3 describedabove and both the input side clutch unit and the output side clutchunit are configured as the dog clutch type in Embodiment 4, the presentinvention is not limited to such configurations.

More specifically, one of the input side clutch unit and the output sideclutch unit can be configured as the friction plate type and the otherside can be configured as the dog clutch type.

FIG. 13 illustrates a hydraulic circuit diagram of a transmissionstructure 5 according to a modification in which the input side clutchunit is configured as the dog clutch type and the output side clutchunit is configured as the friction plate type.

FIG. 14 illustrate a hydraulic pressure waveform charts in thetransmission structure 5 in the switching from the first transmissionstate to the second transmission state.

It is a matter of course that the configuration relating to the doubletransmission structure in Embodiment 3 and 4 described above is alsoapplicable to Embodiment 2 described above.

Embodiment 5

Hereinafter, further yet still another embodiment of the transmissionstructure according to the present invention is described with referenceto the accompanying drawings.

The transmission structure according to this embodiment is differentfrom the transmission structure 3 according to Embodiment 3 describedabove only in the point that the position control timing of theelectromagnetic valves 365(1), 365(2), 367(1) and 367(2) by the controldevice 100 in the switching between the first and second transmissionstates is changed.

FIG. 15 illustrates hydraulic pressure waveform charts of thesupply/discharge lines 360(1), 360(2), 362(1) and 362(2) in theswitching from the first transmission state to the second transmissionstate.

In the state where the speed change operation member 90 is locatedbefore the switching speed position (i.e., in a low speed state wherethe rotational speed of the speed change output shaft 45 is less thanthe switching speed), the control device 100 performs the same positioncontrol as that of Embodiment 3 described above to the electromagneticvalves 365(1), 365(2), 367(1) and 367(2).

More specifically, the control device 100 locates the input side firstelectromagnetic valve 365(1) and the output side first electromagneticvalve 367(1) at the supply position and locates the input side secondelectromagnetic valve 365(2) and the output side second electromagneticvalve 367(2) at the discharge positions.

In this state, while the hydraulic pressure of the input side secondsupply/discharge line 360(2) and the output side second supply/dischargeline 362(2) is released, so that the input side second clutch mechanism60(2) and the output side second clutch mechanism 80(2) are brought intothe disengagement state, the input side first supply/discharge line360(1) and the output side first supply/discharge line 362(1) aremaintained at the engagement hydraulic pressure set by the pilotpressure of the corresponding electromagnetic valves 365(1) and 367(1),so that the input side first clutch mechanism 60(1) and the output sidefirst clutch mechanism 80(1) are brought into the engagement state asillustrated in FIG. 15 .

Thus, the transmission structure is brought into the first transmissionstate.

Also in a state where the speed change operation member 90 exceeds theswitching speed position (i.e., also in the high speed state where therotational speed of the speed change output shaft 45 is equal to orhigher than the switching speed), the control device 100 performs thesame position control as that of Embodiment 3 described above to theelectromagnetic valves 365(1), 365(2), 367(1) and 367(2).

More specifically, the control device 100 locates the input side firstelectromagnetic valve 365(1) and the output side first electromagneticvalve 367(1) at the discharge positions and locates the input sidesecond electromagnetic valve 365(2) and the output side secondelectromagnetic valve 367(2) at the supply positions.

In this state, while the hydraulic pressure of the input side firstsupply/discharge line 360(1) and the output side first supply/dischargeline 362(1) is released, so that the input side first clutch mechanism60(1) and the output side first clutch mechanism 80(1) are brought intothe disengagement state, the input side second supply/discharge line360(2) and the output side second supply/discharge line 362(2) aremaintained at the engagement hydraulic pressure set by the pilotpressure of the corresponding electromagnetic valves 365(2) and 367(2),so that the input side second clutch mechanism 60(2) and the output sidesecond clutch mechanism 80(2) are brought into the engagement state asillustrated in FIG. 15 .

Thus, the transmission structure 3 is brought into the secondtransmission state.

Meanwhile, in the switching between the first and second transmissionstates, the control device 100 performs position control different fromthat of Embodiment 3 described above to the electromagnetic valves365(1), 365(2), 367(1) and 367(2).

More specifically, when recognizing that the speed change operationmember 90 is operated from the zero speed position side to the switchingspeed position at time Ta in FIG. 15 . (i.e., when recognizing that therotational speed of the speed change output shaft 45 reaches theswitching speed from a state where the rotational speed is less than theswitching speed based on a signal from the output sensor 95 b), thecontrol device 100 moves the input side second electromagnetic valve365(2) and the output side second electromagnetic valve 367(2) locatedat the discharge positions at the time before the switching to thesupply positions from the discharge positions while maintaining theinput side first electromagnetic valve 365(1) and the output side firstelectromagnetic valve 367(1) located at the supply positions at the timebefore switching the transmission state (at the time of the firsttransmission state in this example) at the supply positions.

Thus, while the input side first supply/discharge line 360(1) and theoutput side first supply/discharge line 362(1) are maintained at theengagement hydraulic pressure, the hydraulic pressure of the input sidesecond supply/discharge line 360(2) and the output side secondsupply/discharge line 362(2) gradually increase to reach the engagementhydraulic pressure at time Tb.

Herein, when recognizing that the hydraulic pressure of the input sidesecond supply/discharge line 360(2) and the output side secondsupply/discharge line 362(2) to which pressure oil is supplied throughthe input side second electromagnetic valve 365(2) and the output sidesecond electromagnetic valve 367(2), the positions of which are moved tothe supply positions from the discharge positions, reaches switchinghydraulic pressure P less than the engagement hydraulic pressure basedon signals from the corresponding pressure sensors 370(2) and 372(2),the control device 100 moves the input side first electromagnetic valve365(1) and the output side first electromagnetic valve 367(1) located atthe supply positions at the time before the switching from the supplypositions to the discharge positions.

The switching hydraulic pressure P is a hydraulic pressure at which thefriction plate group of the corresponding clutch mechanism is broughtinto a sliding engagement state of performing power transmission whilesliding.

The transmission structure according to this embodiment having such aconfiguration can prevent or reduce the generation of the state wherethe traveling driving force is not transmitted to the driving wheels 220in the switching between the first and second transmission states asmuch as possible and further can effectively prevent or reduce aswitching shock which may occur in the switching between the first andsecond transmission states.

More specifically, the input side first and second speed change ratiosare set so that the rotational speed of the second element when the HSToutput is set to the second HST speed in the first transmission stateand the rotational speed of the second element by the rotation powertransmitted through the input side second transmission mechanism 50(2)in the second transmission state are the same and so that the rotationalspeed of the first element when the HST output is set to the second HSTspeed in the second transmission state and the rotational speed of thefirst element by the rotation power transmitted through the input sidefirst transmission mechanism 50(1) in the first transmission state arethe same.

Therefore, a rotational speed difference theoretically does not occur inthe first element and/or the second element in the switching between thefirst and second transmission states.

However, a rotational speed difference may occur in the first elementand/or the second element in the switching between the first and secondtransmission states due to a manufacturing error and the like.

With respect to this point, in this embodiment, even if a rotationalspeed difference occurs in the first element and/or the second elementin the switching between the first and second transmission states,immediately before one of the clutch mechanisms (the input side secondclutch mechanism 60(2) in the example of FIG. 15 ), to which pressureoil is supplied through the electromagnetic valve (the input side secondelectromagnetic valve 365(2) in the example of FIG. 15 ), the positionof which is moved from the disengagement position to the supply positionin the switching between the first and second transmission states, isbrought into a perfect engagement state by way of processes in which thefriction plate group of the clutch mechanism is graduallyfriction-engaged while sliding, and then the hydraulic pressure of theone clutch mechanism reaches the engagement hydraulic pressure, thehydraulic pressure of the other one of the clutch mechanisms (the inputside first clutch mechanism 60(1) in the example of FIG. 15 ) broughtinto the engagement state before the switching between the first andsecond transmission states is released from the engagement hydraulicpressure.

Therefore, the generation of the state where the traveling driving forceis not transmitted to the driving wheels 220 in the switching betweenthe first and second transmission states can be prevented or reduced asmuch as possible and a damage on a transmission system due to theswitching shock or the double transmission state which may occur in theswitching between the first and second transmission states can beeffectively prevented or reduced.

Moreover, the output side first and second speed change ratios are setso that the rotational speed developed in the speed change output shaft45 when the HST output is set to the second HST speed is same in thefirst and second transmission states.

Therefore, a rotational speed difference theoretically does not occur inthe speed change output shaft 45 in the switching between the first andsecond transmission states.

However, a rotational speed difference occurs in the speed change outputshaft 45 in the switching between the first and second transmissionstates due to a manufacturing error and the like in some cases.

With respect to this point, in this embodiment, even if a rotationalspeed difference occurs in the speed change output shaft 45 in theswitching between the first and second transmission states, immediatelybefore one of the clutch mechanisms (the output side second clutchmechanism 80(2) in the example of FIG. 15 ), to which pressure oil issupplied through the electromagnetic valve (the output side secondelectromagnetic valve 367(2) in the example of FIG. 15 ), the positionof which is moved from the disengagement position to the supply positionin the switching between the first and second transmission states, isbrought into a perfect engagement state by way of processes in which thefriction plate group of the clutch mechanism is graduallyfriction-engaged while sliding, and then the hydraulic pressure of theone clutch mechanism reaches the engagement hydraulic pressure, thehydraulic pressure of the other one of the clutch mechanisms (the outputside first clutch mechanism 80(1) in the example of FIG. 15 ) broughtinto the engagement state before the switching between the first andsecond transmission states is released from the engagement hydraulicpressure.

Therefore, the generation of the state where the traveling driving forceis not transmitted to the driving wheels 220 in the switching betweenthe first and second transmission states can be prevented or reduced asmuch as possible and a damage on the transmission system due to theswitching shock or the double transmission state which may occur in theswitching between the first and second transmission states can beeffectively prevented or reduced.

The configuration in which, immediately before one of the clutchmechanisms is brought into a perfect engagement state from adisengagement state by way of processes in which the electromagneticvalves (the input side second electromagnetic valve 365(2) and theoutput side second electromagnetic valve 367(2) in the example of FIG.15 ) located at the discharge positions at the time before the switchingare moved from the discharge positions to the supply positions whilemaintaining the electromagnetic valves (the input side firstelectromagnetic valve 365(1) and the output side first electromagneticvalve 367(1) in the example of FIG. 15 ) located at the supply positionsat the time before the switching at the supply positions in theswitching between the first and second transmission states, and then thehydraulic pressure of the supply/discharge lines (the input side secondsupply/discharge line 360(2) and the output side second supply/dischargeline 362(2) in the example of FIG. 15 ) to which pressure oil issupplied through the electromagnetic valves, the positions of which aremoved from the discharge positions to the supply positions, reaches theengagement hydraulic pressure, the electromagnetic valves (the inputside first electromagnetic valve 365(1) and the output side firstelectromagnetic valve 367(1) in the example of FIG. 15 ) located at thesupply positions at the time before the switching are moved from thesupply positions to the discharge positions can be applied to only oneof the input side clutch unit formed by the input side first and secondclutch mechanisms 60(1) and 60(2) and the output side clutch unit formedby the output side first and second clutch mechanisms 80(1) and 80(2) inwhich a rotational speed difference may occur due to a manufacturingerror and the like and the dog clutch type illustrated in FIG. 10described above can be adopted to the other clutch unit when the otherclutch unit is free from the possibility or has less possibility,whereby a cost reduction can be achieved.

Embodiment 6

Hereinafter, further yet still another embodiment of the transmissionstructure according to the present invention is described with referenceto the accompanying drawings.

FIG. 16 illustrates a hydraulic circuit diagram of a transmissionstructure 6 according to this embodiment.

In the figure, the same components as those in Embodiments describedabove are designated by the same reference numerals and a descriptionthereof is omitted as appropriate.

In the transmission structure 1 according to Embodiment 1, the inputside first speed change ratio of the input side first transmissionmechanism 50(1) and the input side second speed change ratio of theinput side second transmission mechanism 50(2) are set so that therotational speed of the second element when the HST output is set to thesecond HST speed in the first transmission state and the rotationalspeed of the second element by the rotation power transmitted throughthe input side second transmission mechanism 50(2) in the secondtransmission state are the same and so that the rotational speed of thefirst element when the HST output is set to the second HST speed in thesecond transmission state and the rotational speed of the first elementby the rotation power transmitted through the input side firsttransmission mechanism 50(1) in the first transmission state are thesame, and further the output side first speed change ratio of the outputside first transmission mechanism 70(1) and the output side second speedchange ratio of the output side second transmission mechanism 70(2) areset so that the rotational speed developed in the speed change outputshaft 45 when the HST output is set to the second HST speed is same inthe first and second transmission states.

According to the transmission structure 1 according to Embodiment 1described above, a rotational speed difference theoretically does notoccur in the first element and/or the second element and the speedchange output shaft 45 in the switching between the first and secondtransmission states.

However, the input side first and second speed change ratios cannot beset to the ideal set values described above due to the number of gearteeth configuring the input side first and second transmissionmechanisms 50(1) and 50(2) in some cases.

In such a case, a rotational speed difference occurs in the firstelement and/or a rotational speed difference occurs in the secondelement in the switching between the first and second transmissionstates.

Similarly, the output side first and second speed change ratios cannotbe set to the ideal set values described above due to the number of gearteeth configuring the output side first and second transmissionmechanisms 70(1) and 70(2) in some cases.

In such a case, a rotational speed difference occurs in the speed changeoutput shaft 45 in the switching between the first and secondtransmission states.

In view of this point, the transmission structure 6 according to thisembodiment is configured so that, when a rotational speed differenceoccurs in the first element and/or the second element and the speedchange output shaft 45 in the switching between the first and secondtransmission states, a damage on the transmission system due to theswitching shock or the double transmission state resulting from therotational speed difference can be prevented or reduced as much aspossible.

Specifically, as illustrated in FIG. 16 , the transmission structure 6according to this embodiment has input side first and secondtransmission mechanisms 650(1) and 650(2) in place of the input sidefirst and second transmission mechanisms 50(1) and 50(2) and output sidefirst and second transmission mechanisms 670(1) and 670(2) in place ofthe output side first and second transmission mechanisms 70(1) and 70(2)as compared with the transmission structure 1 according to Embodiment 1described above.

As illustrated in FIG. 16 , the input side first transmission mechanism650(1) has an input side first driving gear 652(1) relatively rotatablycoupled with the main driving shaft 212 and an input side first drivengear 654(1) meshed with the input side first driving gear 652(1) andcoupled with the first element.

The input side second transmission mechanism 650(2) has an input sidesecond driving gear 652(2) relatively rotatably supported by the maindriving shaft 212 and an input side second driven gear 654(2) meshedwith the input side second driving gear 652(2) and coupled with thesecond element.

The output side first transmission mechanism 670(1) has an output sidefirst driving gear 672(1) supported by the speed change intermediateshaft 43 so as not to be relatively rotatable and an output side firstdriven gear 674(1) meshed with the output side first driving gear 672(1)and relatively rotatably supported by the speed change output shaft 45.

The output side second transmission mechanism 670(2) has an output sidesecond driving gear 672(2) coupled with the first element and an outputside second driven gear 674(2) meshed with the output side seconddriving gear 672(2) and relatively rotatably supported by the speedchange output shaft 45.

FIG. 17 illustrates hydraulic pressure waveform charts of thesupply/discharge lines 360(1), 360(2), 362(1) and 362(2) in theswitching from the first transmission state to the second transmissionstate.

In this embodiment, the control device 100 performs the same positioncontrol as that in Embodiment 5 described above to the electromagneticvalves 365(1), 365(2), 367(1) and 367(2) in the switching between thefirst and second transmission states.

More specifically, when recognizing that the rotational speed of thespeed change output shaft 45 reaches the switching speed from the statewhere the rotational speed is less than the switching speed based on asignal from the output sensor 95 b at time Ta in FIG. 17 , the controldevice 100 moves the input side second electromagnetic valve 365(2) andthe output side second electromagnetic valve 367(2) located at thedischarge positions at the time before the switching from the dischargepositions to the supply positions while maintaining the input side firstelectromagnetic valve 365(1) and the output side first electromagneticvalve 367(1) located at the supply positions at the time before theswitching the transmission state (at the time of the first transmissionstate in this example) at the supply positions.

Thus, as illustrated in FIG. 17 , the hydraulic pressure of the inputside second supply/discharge line 360(2) and the output side secondsupply/discharge line 362(2) gradually increases to reach the engagementhydraulic pressure at time Tb while the input side firstsupply/discharge line 360(1) and the output side first supply/dischargeline 362(1) are maintained at the engagement hydraulic pressure.

Herein, when recognizing that the hydraulic pressure of the input sidesecond supply/discharge line 360(2) and the output side secondsupply/discharge line 362(2) to which pressure oil is supplied throughthe input side second electromagnetic valve 365(2) and the output sidesecond electromagnetic valve 367(2), the positions of which are moved tothe supply positions from the discharge positions, reaches the switchinghydraulic pressure P less than the engagement hydraulic pressure basedon signals from the corresponding pressure sensors 370(2) and 372(2),the control device 100 moves the input side first electromagnetic valve365(1) and the output side first electromagnetic valve 367(1) located atthe supply positions at the time before the switching from the supplypositions to the discharge positions.

According to the transmission structure 6 having such a configuration,even if a rotational speed difference occurs in the first element and/orthe second element and the speed change output shaft 45 in the switchingbetween the first and second transmission states, immediately before theclutch mechanisms are brought into a perfect engagement state from adisengagement state by way of processes in which the friction plategroups of the clutch mechanisms (the input side second clutch mechanism60(2) and the output side second clutch mechanism 80(2) in the exampleof FIG. 17 ) to which pressure oil is supplied through theelectromagnetic valves (the input side second electromagnetic valve365(2) and the output side second electromagnetic valve 367(2) in theexample of FIG. 17 ), the positions of which are moved from thedisengagement positions to the supply positions in the switching betweenthe first and second transmission states, are gradually friction-engagedwhile sliding, and then the hydraulic pressure of the clutch mechanismsreaches the engagement hydraulic pressure, the clutch mechanisms (theinput side first clutch mechanism 60(1) and the output side first clutchmechanism 80(1) in the example of FIG. 17 ) brought into the engagementstate before the switching between the first and second transmissionstates are released from the engagement hydraulic pressure.

Therefore, the generation of the state where the traveling driving forceis not transmitted to the driving wheels 220 in the switching betweenthe first and second transmission states can be prevented or reduced asmuch as possible and the switching shock or a damage on the transmissionsystem which may occur in the switching between the first and secondtransmission states can be effectively prevented or reduced.

In this embodiment, the configuration where, when recognizing that,while one electromagnetic valve located at the supply position at thetime before the switching is maintained at the supply position, theother electromagnetic valve located at the discharge position at thetime before the switching is moved from the discharge position to thesupply position in the switching between the first and secondtransmission states, and then the hydraulic pressure of asupply/discharge line to which pressure oil is supplied through theother electromagnetic valve reaches the switching hydraulic pressure Plower than the engagement hydraulic pressure based on a signal from thecorresponding pressure sensor, the one electromagnetic valve is movedfrom the supply position to the discharge position is applied to boththe input side clutch unit formed by the input side first and secondclutch mechanisms 60(1) and 60(2) and the output side clutch unit formedby the output side first and second clutch mechanisms 80(1) and 80(2).However, it is a matter of course that the present invention is notlimited to such an aspect, and the above-described configuration can beapplied to only one of the input side clutch unit and the output sideclutch unit in which a rotational speed difference occurs due to thesetting of the number of gear teeth configuring the transmissionmechanisms and the like and the dog clutch type illustrated in FIG. 10described above can be adopted to the other clutch unit when the otherclutch unit is free from the possibility, whereby a cost reduction canbe achieved.

Moreover, this embodiment is also applicable to the transmissionstructure 2 according to Embodiment 2.

In Embodiments 5 and 6 described above, the hydraulic pressure of theclutch mechanism brought into the engagement state at the time beforethe switching (hereinafter referred to as “engaged clutch mechanismbefore the switching”) is lowered at a substantially fixed rate to bereleased from the engagement hydraulic pressure in the switching betweenthe first and second transmission states. In place of the configuration,as illustrates in FIG. 18 , it is possible to lower the hydraulicpressure of the engaged clutch mechanism before the switching at asubstantially fixed rate in response to the fact that the hydraulicpressure of the clutch mechanism brought into the disengagement state atthe time before the switching (hereafter referred to as “disengagedclutch mechanism before the switching) reaches the switching hydraulicpressure P and then lower the hydraulic pressure of the engaged clutchmechanism before the switching to the release hydraulic pressure at onceat the time when the hydraulic pressure of the disengaged clutchmechanism before the switching reaches the engagement hydraulicpressure, whereby unnecessary sliding transmission state time can bereduced to improve durability of the friction plate.

Also in Embodiments 5 and 6 described above, in place of theconfiguration of detecting the engagement state of the correspondingfriction plate clutch mechanisms by the pressure sensors 370(1), 370(2),372(1) and 372(2), a configuration of detecting the engagement state ofthe corresponding friction plate clutch mechanisms by other clutchengagement detection units detecting a supply current value, supplycurrent time, and the like of the proportional electromagnetic valves365(1), 365(2), 367(1) and 367(2) can also be adopted.

Embodiment 7

Hereinafter, further yet still another embodiment of the transmissionstructure according to the present invention is described with referenceto the accompanying drawings.

FIG. 19 illustrates a transmission schematic view of a working vehicle202 to which a transmission structure 7 according to this embodiment isapplied.

FIG. 20 illustrates a hydraulic circuit diagram of the transmissionstructure 7 according to this embodiment.

In the figure, the same components as those in Embodiments describedabove are designated by the same reference numerals and a descriptionthereof is omitted as appropriate.

The transmission structure 1 according to Embodiment 1 is configured sothat normal and reverse switching of driving force is performed by theforward/reverse movement switching mechanism 230 disposed on thedownstream side in the transmission direction relative to the speedchange output shaft 45.

More specifically, as illustrated in FIG. 1 , the transmission structure1 according to Embodiment 1 has the forward/reverse movement switchingmechanism 230 switching the rotation direction of the driving forcebetween the forward movement direction and the reverse movementdirection between the speed change output shaft 45 and the travelingtransmission shaft 235 operatively rotationally driven by the rotationpower of the speed change output shaft 45.

In contrast thereto, the transmission structure 7 according to thisembodiment is configured to be able to switch the rotation direction ofthe driving force transmitted to the speed change output shaft 45between the normal direction and the reverse direction.

Specifically, as illustrated in FIG. 19 , the transmission structure 7has the HST 10, the planetary gear mechanism 30, the input side firstand second transmission mechanisms 50(1) and 50(2), the input side firstand second clutch mechanisms 60(1) and 60(2), the output side firsttransmission mechanism 70(1) (forward movement first transmissionmechanism) capable of operatively transmitting the rotation power of thesecond element to the speed change output shaft 45 in the normalrotation state, the output side second transmission mechanism 70(2)(forward movement second transmission mechanism) capable of operativelytransmitting the rotation power of the first element to the speed changeoutput shaft 45 in the normal rotation state, a reverse movementtransmission mechanism 70(R) capable of operatively transmitting therotation power of the second element to the speed change output shaft 45in the reverse rotation state, the output side first clutch mechanism80(1) (forward movement first clutch mechanism), the output side secondclutch mechanism 80(2), and a reverse movement clutch mechanism 80(R)engaging/disengaging the power transmission of the output side firsttransmission mechanism 70(1) (forward movement first transmissionmechanism), the output side second transmission mechanism 70(2) (forwardmovement second transmission mechanism), and the reverse movementtransmission mechanism 70(R), respectively, the speed change operationmember 90, the HST sensor 95 a, the output sensor 95 b, and the controldevice 100.

The reverse movement transmission mechanism 70(R) has a reverse movementdriving gear 72(R) supported by the speed change intermediate shaft 43so as not to be relatively rotatable, a reverse movement driven gear74(R) relatively rotatably supported by the speed change output shaft45, and a reverse movement idle gear 73(R) meshed with the reversemovement driving gear 72(R) and the reverse movement driven gear 74(R).

The reverse movement clutch mechanism 80(R) has a reverse movementclutch housing 82(R) supported by the speed change output shaft 45 so asnot to be relatively rotatable, a reverse movement friction plate group84(R) containing a reverse movement driving side friction platesupported by the reverse movement driven gear 74(R) so as not to berelatively rotatable and a reverse movement driven side friction platesupported by the reverse movement clutch housing 82(R) so as not to berelatively rotatable in a state of being opposed to the reverse movementdriving side friction plate, and a reverse movement piston (notillustrated) frictionally-engaging the reverse movement friction plategroup 84(R).

The reference numeral 105 in FIG. 19 designates an electromagnetic valveunit containing the input side first electromagnetic valve 365(1) andthe like.

The reference numeral 242 in FIG. 19 is a sub speed change mechanismcontaining the friction plate clutch mechanism and is provided in placeof the sub speed change mechanism 240 containing the dog clutch typeclutch mechanism in the transmission structure 1 according to Embodiment1.

The control device 100

-   develops a forward movement first transmission state where the input    side first clutch mechanism 60(1) and the output side first clutch    mechanism 80(1) are brought into the engagement state in a state    where the speed change operation member 90 is located between the    zero speed position and the switching speed position (i.e., in a low    speed state where the rotational speed of the speed change output    shaft 45 is from the zero speed to speed less than the switching    speed in the forward movement direction based on detection signals    of the HST sensor 95 a and the output sensor 95 b)-   develops a forward movement second transmission state where the    input side second clutch mechanism 60(2) and the output side second    clutch mechanism 80(2) are brought into the engagement state in a    state where the speed change operation member 90 is operated beyond    the switching speed position (i.e., in a high speed state where the    rotational speed of the speed change output shaft 45 is equal to or    higher than the switching speed in the forward movement direction),    and-   develops the reverse movement transmission state where the input    side first clutch mechanism 60(1) and the reverse movement clutch    mechanism 80(R) are brought into the engagement state in a state    where the speed change operation member 90 is operated from the zero    speed position to the reverse movement side (i.e., in a reverse    movement transmission state where the rotational speed of the speed    change output shaft 45 changes from the zero speed to the reverse    movement side).

FIGS. 21A and 21B illustrate graphs illustrating the relationshipbetween the traveling vehicle speed and the HST output in the workingvehicle 202 to which the transmission structure 7 according to thisembodiment is applied.

FIGS. 21A and 21B illustrate graphs in states where the sub speed changemechanism 242 is engaged with a low speed stage and a high speed stage,respectively.

As illustrated in FIGS. 21A and 21B, the control device 100 operates theoutput adjustment member 20 so that the HST output is speed-changed fromthe first HST speed toward the second HST speed in response to a forwardmovement side acceleration operation of the speed change operationmember 90 in the forward movement first transmission state.

More specifically, when the speed change operation member 90 is operatedbetween the zero speed position and the forward movement side switchingspeed position, the control device 100 develops the forward movementfirst transmission state, and then operates the output adjustment member20 so that the HST output is speed-changed from the side of the firstHST speed to the side of the second HST speed as the accelerationoperation of the speed change operation member 90 is performed from thezero speed position side to the forward movement side switching speedposition.

In the forward movement second transmission state, the control device100 operates the output adjustment member 20 so that the HST output isspeed-changed from the second HST speed toward the first HST speed inresponse to the forward movement side acceleration operation of thespeed change operation member 90.

More specifically, when recognizing that the speed change operationmember 90 is operated from the zero speed position side to the forwardmovement side switching speed position, the control device 100 performsswitching from the forward movement first transmission state to theforward movement second transmission state, and develops the forwardmovement second transmission state when the speed change operationmember 90 is located on the forward movement high speed side relative tothe forward movement side switching speed position, and then operatesthe output adjustment member 20 so that the HST output is speed-changedfrom the second HST speed toward the first HST speed in response to theforward movement side acceleration operation of the speed changeoperation member 90.

In the reverse movement transmission state, the control device 100operates the output adjustment member 20 so that the HST output isspeed-changed from the first HST speed toward the second HST speed inresponse to the reverse movement side acceleration operation of thespeed change operation member 90.

More specifically, when the speed change operation member 90 is operatedfrom the zero speed position to the reverse movement side, the controldevice 100 develops the reverse movement transmission state, and thenoperates the output adjustment member 20 so that the HST output isspeed-changed from the side of the first HST speed to the side of thesecond HST speed as a reverse movement acceleration operation of thespeed change operation member 90 is performed.

As illustrated in FIG. 21 , this embodiment is also configured so that aspeed difference does not occur in the traveling speed (i.e., the speedchange output shaft 45) in the switching between the forward movementside first and second transmission states in the same manner as inEmbodiment 1.

Specifically, the speed change ratio (input side first speed changeratio) of the input side first transmission mechanism 50(1) and thespeed change ratio (input side second speed change ratio) of the inputside second transmission mechanism 50(2) are set so that the rotationalspeed of the second element when the HST output is set to the second HSTspeed in the forward movement first transmission state and therotational speed of the second element by the rotation power transmittedthrough the input side second transmission mechanism 50(2) in theforward movement second transmission state are the same and so that therotational speed of the first element when the HST output is set to thesecond HST speed in the forward movement second transmission state andthe rotational speed of the first element by the rotation powertransmitted through the input side first transmission mechanism 50(1) inthe forward movement first transmission state are the same.

The speed change ratio (forward movement first speed change ratio) ofthe output side first transmission mechanism 70(1) (forward movementfirst transmission mechanism) and the speed change ratio (forwardmovement second speed change ratio) of the output side secondtransmission mechanism 70(2) (forward movement second transmissionmechanism) are set so that the rotational speed developed in the speedchange output shaft 45 when the HST output is set to the second HSTspeed is same in the first and second transmission states.

According to such a configuration, the occurrence of a rotational speeddifference in the speed change output shaft 45 in the switching betweenthe forward movement side first and second transmission states, i.e.,the occurrence of a traveling speed difference, can be effectivelyprevented or reduced.

The HST 10 and the planetary gear mechanism 30 are set so that, when theHST output is set to the first HST speed in the engagement state of theinput side first clutch mechanism 60(1), the rotational speed of thesecond element becomes the zero speed.

According to such a configuration, the forward/reverse movementswitching of a vehicle can be smoothly performed. In particular, theconfiguration is effective in the case of a working vehicle performingwork frequently requiring forward/reverse movement switching.

Next, the pressure oil supply/discharge configuration of thetransmission structure 7 is described.

As illustrated in FIG. 20 , the transmission structure 7 has thepressure oil supply line 155, the input side first supply/discharge line360(1), the input side second supply/discharge line 360(2), the outputside first supply/discharge line 362(1) (forward movement side firstsupply/discharge line), the output side second supply/discharge line362(2) (forward movement side second supply/discharge line), a reversemovement supply/discharge line 364 supplying/discharging pressure oil tothe reverse movement clutch mechanism 80(R), a forward movement supplyline 310(F), a reverse movement supply line 310(R), the input side firstelectromagnetic valve 365(1), the input side second electromagneticvalve 365(2), the output side first electromagnetic valve 367(1), andthe output side second electromagnetic valve 367(2), the input sidefirst pressure sensor 370(1) and the input side second pressure sensor370(2), the output side first pressure sensor 372(1) and the output sidesecond pressure sensor 372(2), a check valve 320 interposed in the inputside first supply/discharge line 360(1), a pilot valve 330 interposed inthe reverse movement supply line 310(R), the drain line 157, and aforward/reverse movement switching electromagnetic valve 300.

In this embodiment, the input side first electromagnetic valve 365(1),the input side second electromagnetic valve 365(2), the output sidefirst electromagnetic valve 367(1) and the output side secondelectromagnetic valve 367(2) are interposed between the forward movementsupply line 310(F) and the input side first supply/discharge line360(1), the input side second supply/discharge line 360(2), the outputside first supply/discharge line 362(1) (forward movement side firstsupply/discharge line) and the output side second supply/discharge line362(2) (forward movement side second supply/discharge line),respectively, and configured to drain the corresponding supply/dischargelines 360(1), 360(2), 362(1) and 362(2) when located at the dischargepositions and meanwhile, fluid-connect the correspondingsupply/discharge lines 360(1), 360(2), 362(1) and 362(2) to the forwardmovement supply line 310(F) when located at the supply positions.

The position of the forward/reverse movement switching electromagneticvalve 300 is controlled by the control device 100 so as to be able totake a forward movement position F where the forward movement supplyline 310(F) is fluid-connected to the pressure oil supply line 155 andthe reverse movement supply line 310(R) is fluid-connected to the drainline 157, a reverse movement position R where the reverse movementsupply line 310(R) is fluid-connected to the pressure oil supply line155 and the forward movement supply line 310(F) is fluid-connected tothe drain line 157, and a neutral position N where the pressure oilsupply line 155, the forward movement supply line 310(F), and thereverse movement supply line 310(R) are fluid-connected to the drainline 157.

The check valve 320 is interposed in the input side firstsupply/discharge line 360(1) to, while permitting that pressure oilsupplied from the forward movement supply line 310(F) through the inputside first electromagnetic valve 365(1) to flow toward the input sidefirst clutch mechanism 60(1) in a pressure oil supply direction, preventthe flow in a pressure oil discharge direction opposite thereto.

In the reverse movement supply line 310(R), the upstream side close tothe hydraulic source 150 is fluid-connected to a secondary side of theforward/reverse movement switching electromagnetic valve 300 and thedownstream side on the side opposite to the hydraulic source 150 isfluid-connected to the input side first supply/discharge line 360(1) onthe downstream side in the pressure oil supply direction relative to thecheck valve 320.

The pilot valve 330 is configured to be able to selectively take acommunication position where the reverse movement supply line 310(R) ismade to communicate and a check position where, while the flow of thepressure oil of the reverse movement supply line 310(R) in the pressureoil supply direction is permitted, the reverse flow is prevented.

The pilot valve 330 is configured to use the hydraulic pressure of theforward movement supply line 310(F) as pilot pressure while beingenergized toward the communication position by a biasing member 332 andto be located at the check position against the pressing force of thebiasing member 332 when pressure oil is supplied to the forward movementsupply line 310(F).

In the reverse movement supply/discharge line 364, the upstream side isfluid-connected to the reverse movement supply line 310(R) on theupstream side in the pressure oil supply direction relative to the pilotvalve 330 and the downstream side is fluid-connected to the reversemovement clutch mechanism 80(R).

The pressure oil supply/discharge configuration of the transmissionstructure 7 operates as follows.

When the speed change operation member 90 is located at the zero speedposition, the control device 100 locates the forward/reverse movementswitching electromagnetic valve 300 at the neutral position.

In this state, the input side first supply/discharge line 360(1), theinput side second supply/discharge line 360(2), the output side firstsupply/discharge line 362(1), the output side second supply/dischargeline 362(2), and the reverse movement supply/discharge line 364 are allopened and all the clutch mechanisms 60(1), 60(2), 80(1), 80(2), and80(R) are brought into the disengagement state, so that power is nottransmitted to the speed change output shaft 45.

When the speed change operation member 90 is operated to the forwardmovement side, the control device 100 locates the forward/reversemovement switching electromagnetic valve 300 at the forward movementposition F before the HST 10 outputs the first HST speed.

Thus, the reverse movement supply line 310(R) is fluid-connected to thedrain line 157 and the forward movement supply line 310(F) isfluid-connected the pressure oil supply line 155.

At this time, the pilot valve 330 is located at the check position bythe hydraulic pressure of the supply line in forward 310 (F). Therefore,the input side first supply/discharge line 360(1) is brought into astate where the hydraulic pressure is held.

When the speed change operation member 90 is operated from the zerospeed position to the forward movement side switching speed position,the control device 100 locates the input side first electromagneticvalve 365(1) and the output side first electromagnetic valve 367(1) atthe supply positions.

Thus, pressure oil flows into the input side first supply/discharge line360(1) and the output side first supply/discharge line 362(1) from theforward movement supply line 310(F), so that the forward movement firsttransmission state where the input side first clutch mechanism 60(1) andthe output side first clutch mechanism 80(1) are brought into theengagement state is developed.

At this time, the input side second supply/discharge line 360(2) and theoutput side second supply/discharge line 362(2) are drained by thecorresponding electromagnetic valves 365(2) and 367(2) and the reversemovement supply/discharge line 364 is drained through the reversemovement supply line 310(R) and the forward/reverse movement switchingelectromagnetic valve 300.

When the speed change operation member 90 is operated to the forwardmovement high speed side beyond the forward movement side switchingspeed position, the control device 100 locates the input side secondelectromagnetic valve 365(2) and the output side second electromagneticvalve 367(2) at the supply positions while locating the input side firstelectromagnetic valve 365(1) and the output side first electromagneticvalve 367(1) at the discharge positions before the HST 10 outputs thesecond HST speed.

Thus, pressure oil flows into the input side second supply/dischargeline 360(2) and the output side second supply/discharge line 362(2) fromthe forward movement supply line 310(F), so that the forward movementsecond transmission state is developed where the input side secondclutch mechanism 60(2) and the output side second clutch mechanism 80(2)are brought into the engagement state.

At this time, the input side first supply/discharge line 360(1) and theoutput side first supply/discharge line 362(1) are drained through thecorresponding electromagnetic valves 365(1) and 367(1) and the reversemovement supply/discharge line 364 is drained through the reversemovement supply line 310(R) and the forward/reverse movement switchingelectromagnetic valve 300.

When the speed change operation member 90 is operated to the reversemovement side, the control device 100 locates the forward/reversemovement switching electromagnetic valve 300 at the reverse movementposition R before the HST 10 outputs the first HST speed.

Thus, the forward movement supply line 310(F) is fluid-connected to thedrain line 157 and the reverse movement supply line 310(R) isfluid-connected to the pressure oil supply line 155.

At this time, the input side first electromagnetic valve 365(1), theinput side second electromagnetic valve 365(2), the output side firstelectromagnetic valve 367(1), and the output side second electromagneticvalve 367(2) are all located at the discharge positions.

Therefore, the input side second supply/discharge line 360(2), theoutput side first supply/discharge line 362(1), and the output sidesecond supply/discharge line 362(2) are opened by the correspondingelectromagnetic valves 365(2), 367(1), and 367(2), respectively.

Meanwhile, the input side first supply/discharge line 360(1) isfluid-connected to the reverse movement supply line 310(R) on thedownstream side in the pressure oil supply direction relative to thecheck valve 320.

Therefore, although the input side first electromagnetic valve 365(1) islocated at the discharge position, pressure oil is supplied to the inputside first supply/discharge line 360(1) through the reverse movementsupply line 310(R), so that the input side first clutch mechanism 60(1)is brought into the engagement state.

At this time, the forward movement supply line 310(F) is opened, andtherefore the pilot valve 330 using the hydraulic pressure of theforward movement supply line 310(F) as pilot pressure is located at thecommunication position by the pressing force of the biasing member 332.

Therefore, pressure oil is effectively supplied to the input side firstsupply/discharge line 360(1) through the reverse movement supply line310(R).

As described above, the reverse movement supply/discharge line 364 isfluid-connected to the reverse movement supply line 310(R) on theupstream side in the pressure oil supply direction relative to the pilotvalve 300 and receives the pressure oil supply from the reverse movementsupply line 310(R).

Thus, the reverse movement transmission state is developed where theinput side first clutch mechanism 60(1) is brought into the engagementstate and the reverse movement clutch mechanism 80(R) is brought intothe engagement state.

With respect to the switching control timing of the input side firstelectromagnetic valve 365(1) and the input side second electromagneticvalve 365(2) and the switching control timing of the output side firstelectromagnetic valve 367(1) and the output side second electromagneticvalve 367(2) in the switching between the forward movement side firstand second transmission states, various embodiments, such as Embodiment3 described above, Embodiment 5 described above, and Embodiment 6described above, are applicable.

As illustrated in FIG. 20 , in this embodiment, the input side firstclutch mechanism 60(1), the input side second clutch mechanism 60(2),the output side first clutch mechanism 80(1), the output side secondclutch mechanism 80(2), and the reverse movement clutch mechanism 80(R)are all configured as a hydraulic friction plate type.

In place of the configuration, at least one of the input side clutchunit formed by the input side first and second clutch mechanisms and theoutput side clutch unit formed by the output side first and secondclutch mechanisms can be configured as the dog clutch type in Embodiment4 described above.

FIG. 22 illustrates a hydraulic circuit diagram of a transmissionstructure 7B according to a modification of this embodiment.

In the figure, the same members as those in Embodiments described aboveare designated by the same reference numerals and a description thereofis omitted as appropriate.

The transmission structure 7B has the input side clutch unit 410 of thedog clutch type in place of the input side first and second clutchmechanisms 60(1) and 60(2) of the friction plate type as compared withthe transmission structure 7 according to this embodiment.

It is a matter of course that the output side clutch unit 430 of the dogclutch type can be provided in place of the output side first and secondclutch mechanisms 80(1) and 80(2) and the clutch mechanism of the dogclutch type can also be provided in place of the reverse movement clutchmechanism 80(R).

Embodiment 8

Hereinafter, further yet still another embodiment of the transmissionstructure according to the present invention is described with referenceto the accompanying drawings.

FIG. 23 illustrates a transmission schematic view of a working vehicle203 to which a transmission structure 8 according to this embodiment isapplied.

FIG. 24 illustrates a partial vertical cross-sectional side view of theworking vehicle 203.

In the figures, the same components as those in Embodiments describedabove are designated by the same reference numerals and a descriptionthereof is omitted as appropriate.

As illustrated in FIG. 23 , the transmission structure 8 according tothis embodiment is further provided with an output side thirdtransmission mechanism 70(3) and an output side third clutch mechanism80(3) as compared with the transmission structure 1 according toEmbodiment 1 described above.

More specifically, the transmission structure 8 is provided with the HST10, the planetary gear mechanism 30, the speed change output shaft 45,the input side first and second transmission mechanisms 50(1) and 50(2),the input side first and second clutch mechanisms 60(1) and 60(2), theoutput side first to third transmission mechanisms 70(1) to 70(3), theoutput side first to third clutch mechanisms 80(1) to 80(3), the speedchange operation member 90, the HST sensor 95 a, the output sensor 95 b,and the control device 100.

In this embodiment, the clutch mechanisms 60(1), 60(2), and 80(1) to80(3) are configured as hydraulic friction plate clutch units.

The output side third transmission mechanism 70(3) is configured to beable to transmit the rotation power of the first element (the internalgear 36 in this embodiment) to the speed change output shaft 45 at anoutput side third speed change ratio where the speed change output shaft45 is rotated at rotational speed higher than the rotational speed atthe output side second speed change ratio of the output side secondtransmission mechanism 70(2).

The output side third clutch mechanism 80(3) is configured toengage/disengage the power of the output side third transmissionmechanism 70(3).

FIG. 25 illustrates a graph illustrating the relationship between thetraveling vehicle speed and the HST output in the working vehicle 203 towhich the transmission structure 8 according to this embodiment isapplied.

As illustrated in FIG. 25 , in this embodiment, the control device 100

-   develops a first transmission state where, while the input side    first clutch mechanism 60(1) is brought into the engagement state    and the input side second clutch mechanism 60(2) is brought into the    disengagement state, the output side first clutch mechanism 80(1) is    brought into the engagement state and the remaining output side    second and third clutch mechanisms 80(2) and 80(3) are brought into    the disengagement state in a state where the speed change operation    member 90 is located between the zero speed position and the first    switching speed position (i.e., in a low speed state where the    rotational speed of the speed change output shaft 45 is from the    zero speed to speed less than the first switching speed based on    detection signals of the HST sensor 95 a and the output sensor 95    b),-   develops a second transmission state where, while the input side    first clutch mechanism 60(1) is brought into the disengagement state    and the input side second clutch mechanism 60(2) is brought into the    engagement state, the output side second clutch mechanism 80(2) is    brought into the engagement state and the remaining output side    first and third clutch mechanisms 80(1) and 80(3) are brought into    the disengagement state in a state where the speed change operation    member 90 is located between the first switching speed position and    the second switching speed position. (i.e., in the intermediate    speed state where the rotational speed of the speed change output    shaft 45 is from the first switching speed to the second switching    speed based on detection signals of the HST sensor 95 a and the    output sensor 95 b), and-   develops a third transmission state where, while the input side    first clutch mechanism 60(1) is brought into the disengagement state    and the input side second clutch mechanism 60(2) is brought into the    engagement state, the output side third clutch mechanism 80(3) is    brought into the engagement state and the remaining output side    first and second clutch mechanisms 80(1) and 80(2) are brought into    the disengagement state in a state where the speed change operation    member 90 is operated beyond the second switching speed position    (i.e., in a high speed state where the rotational speed of the speed    change output shaft 45 exceeds the second switching speed based on    detection signals of the HST sensor 95 a and the output sensor 95    b).

As illustrated in FIG. 23 , the transmission structure 8 has theforward/reverse movement switching mechanism 230 interposed between thespeed change output shaft 45 and the traveling transmission shaft 235,in which the output of the forward/reverse movement switching mechanism230 is operatively transmitted to the traveling transmission shaft 235.

Then, the control device 100 brings the forward/reverse movementswitching mechanism 230 into a forward movement transmission state and areverse movement transmission state in response to an operation to theforward movement side and the reverse movement side of the speed changeoperation member 90, respectively.

More specifically, in the working vehicle 203, when the speed changeoperation member 90 is operated between the zero speed position and aforward movement side first switching speed position, the forwardmovement first transmission state is developed, and, when the speedchange operation member 90 is located at the forward movement side firstswitching speed position, the traveling transmission shaft 235 rotatesat rotational speed setting the traveling vehicle speed to +a.

When the speed change operation member 90 is operated between theforward movement side first switching speed position and a forwardmovement side second switching speed position, the forward movementsecond transmission state is developed and, when the speed changeoperation member 90 is located at the forward movement side secondswitching speed position, the traveling transmission shaft 235 rotatesat rotational speed setting the traveling vehicle speed to +b.

Then, when the speed change operation member 90 is operated beyond theforward movement side second switching speed position, a forwardmovement third transmission state is developed and, when the speedchange operation member 90 is located at a forward movement side maximumspeed position, the traveling transmission shaft 235 rotates atrotational speed setting the traveling vehicle speed to +c.

Similarly, when the speed change operation member 90 is operated betweenthe zero speed position and a reverse movement side first switchingspeed position, a reverse first transmission state is developed and,when the speed change operation member 90 is located at the reversemovement side first switching speed position, the traveling transmissionshaft 235 rotates at rotational speed setting the traveling vehiclespeed to −a.

When the speed change operation member 90 is operated between thereverse movement side first switching speed position and a reversemovement side second switching speed position, a reverse movement secondtransmission state is developed and, when the speed change operationmember 90 is located at the reverse movement side second switching speedposition, the traveling transmission shaft 235 rotates at rotationalspeed setting the traveling vehicle speed to −b.

Then, when the speed change operation member 90 is operated beyond thereverse movement side second switching speed position, a reversemovement third transmission state is developed and, when the speedchange operation member 90 is located at a reverse movement side maximumspeed position, the traveling transmission shaft 235 rotates atrotational speed setting the traveling vehicle speed to −c.

In the same manner as in Embodiment 1 described above, the input sidefirst speed change ratio of the input side first transmission mechanism50(1) and the input side second speed change ratio of the input sidesecond transmission mechanism 50(2) are set so that the rotational speedof the second element (the carrier 38 in this embodiment) when the HSToutput is set to the second HST speed in the first transmission stateand the rotational speed of the second element by the rotation powertransmitted through the input side second transmission mechanism 50(2)in the second transmission state are the same and so that the rotationalspeed of the first element (the internal gear 36 in this embodiment)when the HST output is set to the second HST speed in the secondtransmission state and the rotational speed of the first element by therotation power transmitted through the input side first transmissionmechanism 50(2) in the first transmission state are the same.

As illustrated in FIG. 25 , the output side first speed change ratio ofthe output side first transmission mechanism 70(1) and the output sidesecond speed change ratio of the output side second transmissionmechanism 70(2) are set so that the rotational speed developed in thespeed change output shaft 45 when the HST output is set to the secondHST speed is same in the first and second transmission states.

As illustrated in FIG. 25 , the transmission structure 8 according tothis embodiment is configured so that the control device 100 operatesthe output adjustment member 20 so that the rotational speed developedin the speed change output shaft 45 in a transmission state after theswitching coincides with or approaches the rotational speed developed inthe speed change output shaft 45 in a transmission state before theswitching in the switching between the second and third transmissionstates.

More specifically, when the speed change operation member 90 is operatedin the acceleration direction under the second transmission state toreach the second switching speed position (when the rotational speed ofthe speed change output shaft 45 reaches the second switching speed),while the control device 100 shifts the output side second clutchmechanism 80(2) from the engagement state to the disengagement state andshifts the output side third clutch mechanism 80(3) from thedisengagement state to the engagement state, the control device 100operates the output adjustment member 20 so that the output of the HST10 is speed-changed from the rotational speed (first HST speed) rotatingthe speed change output shaft 45 at the second switching speed under thesecond transmission state to the rotational speed (third HST speed ofFIG. 25 ) rotating the speed change output shaft 45 at the secondswitching speed or speed around the second switching speed under thethird transmission state.

When the speed change operation member 90 is operated in a decelerationdirection under the third transmission state to reach the secondswitching speed position (when the rotational speed of the speed changeoutput shaft 45 reaches the second switching speed), while the controldevice 100 shifts the output side third clutch mechanism 80(3) to thedisengagement state from the engagement state and shifts the output sidesecond clutch mechanism 80(2) to the engagement state from andisengagement state, the control device 100 operates the outputadjustment member 20 so that the output of the HST 10 is speed-changedfrom the rotational speed (third HST speed) rotating the speed changeoutput shaft 45 at second switching speed under the third transmissionstate to the rotational speed (first HST speed) rotating the speedchange output shaft 45 at the second switching speed or speed around thesecond switching speed under the second transmission state.

The transmission structure 8 having such a configuration can extend thespeed changeable range (speed change region) while obtaining the sameeffects as those of the transmission structure according to Embodiment 1described above.

In this embodiment, the output side first and second speed change ratiosare set so that the rotational speed developed in the speed changeoutput shaft 45 when the HST output is set to the second HST speed issame in the first and second transmission states as described above.However, in place of the configuration, a configuration may beacceptable in which the control device 100 operates the outputadjustment member 20 so that, in the switching between the first andsecond transmission states, the rotational speed developed in the speedchange output shaft 45 in a transmission state after the switchingcoincides with or approaches the rotational speed developed in the speedchange output shaft 45 in the transmission state before the switching.

As illustrated in FIG. 23 and FIG. 24 , the transmission structure 8according to this embodiment has a speed change transmission shaft 44externally inserted in a relatively rotatable manner into the speedchange intermediate shaft 43 coupled with the second element (thecarrier 38 in this embodiment) so as not to be relatively rotatablearound the axis.

The speed change transmission shaft 44 is configured to be coupled withthe first element (the internal gear 36 in this embodiment) so as not tobe relatively rotatable around the axis, the input side firsttransmission mechanism 50(1) is configured to operatively transmit therotation power of the main driving shaft 212 to the first elementthrough the speed change transmission shaft 44, and the output sidefirst and second transmission mechanisms 70(1) and 70(2) are configuredto operatively transmit the rotation power of the first element to thespeed change output shaft 45 through the speed change transmission shaft44.

In detail, as illustrated in FIG. 23 and FIG. 24 , the input side firstdriven gear 54(1) of the input side first transmission mechanism 50(1)is supported by the speed change transmission shaft 44 so as not to berelatively rotatable in a state of being operatively coupled with theinput side first driving gear 52(1) relatively rotatably supported bythe main driving shaft 212 in this embodiment.

The output side second driving gear 72(2) of the output side secondtransmission mechanism 70(2) is supported by the speed changetransmission shaft 44 so as not to be relatively rotatable in a state ofbeing operatively coupled with the output side second driven gear 74(2).

The output side third transmission mechanism 70(3) has an output sidethird driving gear 72(3) supported by the speed change transmissionshaft 44 so as not to be relatively rotatable and an output side thirddriven gear 74(3) operatively coupled with the output side third drivinggear 72(3) and relatively rotatably supported by the speed change outputshaft 45.

The input side second transmission mechanism 50(2) has the input sidesecond driving gear 52(2) relatively rotatably supported by the maindriving shaft 212 and the input side first driven gear 54(2) operativelycoupled with the input side second driving gear 52(2) and maderelatively unrotatable to the second element in the same manner as inEmbodiment 1 described above.

As illustrated in FIG. 24 , the transmission structure 8 has a variableinput shaft 31 supporting the third element (the sun gear 32 in thisembodiment) functioning as the variable power input portion so as not tobe relatively rotatable around the axis and the input side first drivengear 54(2) is relatively rotatably supported by the variable input shaft31.

The variable input shaft 31 supports a driven gear 216 b of the geartrain 216 operatively transmitting the rotation power of the motor shaft16 to the third element (the sun gear 32) so as not to be relativelyrotatable.

In this embodiment, the output side third clutch mechanism 80(3) has anoutput side clutch housing 83 supported by the speed change output shaft45 so as not to be relatively rotatable, an output side third frictionplate group 84(3) containing a third driving side friction platesupported by the output side third driven gear 74(3) so as not berelatively rotatable and a third driven side friction plate supported bythe output side clutch housing 83 so as not to be relatively rotatablein a state of being opposed to the third driving side friction plate,and an output side third piston (not illustrated) frictionally engagingthe output side third friction plate group 84(3).

As illustrated in FIG. 24 , the transmission structure 8 according tothis embodiment is housed in a housing structure 500 in the workingvehicle 203.

The housing structure 500 has a front housing 510 and a rear housing 550coupled in series.

The front housing 510 has a hollow front housing body 512, a frontsupporting wall 514 and a second supporting wall 518 extended radiallyinward from the inner surface at an intermediate position in thelongitudinal direction of the front housing body 512, and a frontbearing plate 516 detachably coupled with a boss portion formed toproject radially inward from the inner surface near a rear opening ofthe front housing body 512.

The rear housing 550 has a hollow rear housing body 552 detachablycoupled with the front housing body 512, a rear bearing plate 554detachably coupled with a boss portion formed to project radially inwardfrom the inner surface near a front opening of the rear housing body552, and a rear supporting wall 556 extended radially inward from theinner surface at an intermediate position in the longitudinal directionof the rear housing body 552.

In such a configuration, the main driving shaft 212 is supported by thefront supporting wall 514, the front bearing plate 516, and the rearbearing plate 554 so as to be rotatable around the axis and the inputside first and second clutch mechanisms 60(1) and 60(2) are supported bythe main driving shaft 212 in the front housing body 512. A relaycylinder portion 516 a for supplying/discharging pressure oil to/fromthe input side first and second clutch mechanisms 60(1) and 60(2) isintegrally formed in the front bearing plate 516 fitted onto the maindriving shaft 212.

To the relay cylinder portion 516 a, the input side first and secondsupply/discharge lines 360(1) and 360(2) illustrated in FIG. 16described above are connected using a means, such as a pipe.

The variable input shaft 31 is configured as a hollow shaft integrallyformed in a rotation center portion of the driven gear 216 b and thefront end side is supported by the front supporting wall 514 so as to berotatable around the axis.

In a sun gear shaft 32 a integrally having the sun gear 32 on the rearend side, the front end side is inserted into the rear end side of thevariable input shaft 31 to be spline-coupled therewith and theintermediate poartion in the axial direction relatively rotatablysupports the input side second driven gear 54(2).

The speed change intermediate shaft 43 is disposed coaxially with thevariable input shaft 31 and the sun gear shaft 32 a. The speed changeintermediate shaft 43 integrally has the carrier 38 on the front endside and the carrier 38 is coupled with the input side second drivengear 54(2) through a bolt. Thus, the front end side of the speed changeintermediate shaft 43 is supported by the front bearing plate 516through the sun gear shaft 32 a and the speed change input shaft 31 soas to be rotatable around the axis and the rear end side of the speedchange intermediate shaft 43 is supported by the rear bearing plate 554so as to be rotatable around the axis.

The hollow speed change transmission shaft 44 externally inserted intothe speed change intermediate shaft 43 in a relatively rotatable mannerintegrally has the internal gear 36 in a front end portion, the frontend side thereof is supported by the front supporting wall 514 throughthe speed change intermediate shaft 43, and the rear end side thereof issupported by the front bearing plate 516. Then, the output side thirddriving gear 72(3), the input side first driven gear 54(1), and theoutput side second driving gear 72(2) are spline-fitted onto the outerperiphery of an intermediate portion reaching the front bearing plate516 from the internal gear 36 of the speed change transmission shaft 44.

The speed change output shaft 45 is supported by the second supportingwall 518, the rear bearing plate 554, and the rear supporting wall 556so as to be rotatable around the axis. The first traveling transmissionshaft 235 is supported by the rear bearing plate 554 and the rearsupporting wall 556 so as to be rotatable around the axis.

The speed change output shaft 45 supports the output side third clutchmechanism 80(3) on the front end side, supports the output side firstand second clutch mechanisms 80(1) and 80(2) in an intermediate portion,and supports the clutch mechanism of the forward/reverse movementswitching mechanism 230 on the rear end side, respectively. Thehydraulic friction plate clutch unit is used also for the clutchmechanism of the forward/reverse movement switching mechanism 230. Arelay cylinder portion 556 a for supplying/discharging pressure oilto/from the five clutch mechanisms arranged on the speed change outputshaft 45 is mounted on the rear supporting wall 556 and fitted to a rearend portion of the speed change output shaft 45.

In a rear half portion not illustrated of the rear housing 550, thedifferential mechanism 260, the PTO clutch mechanism 285, and the PTOmultistage speed change mechanism 290 are housed.

In this embodiment, although the input side first and second clutchmechanisms 60(1) and 60(2) and the output side first to third clutchmechanisms 80(1) to 80(3) are all configured as the friction plate type,some or all thereof can be configured as the dog clutch type.

FIG. 26 illustrates a transmission schematic view of a working vehicle203 to which a transmission structure 8B according to a modification ofthis embodiment provided with the input side clutch unit 410 of the dogclutch type in place of the input side first and second clutchmechanisms 60(1) and 60(2) of the friction plate type is applied.

Embodiment 9

Hereinafter, further yet still another embodiment of the transmissionstructure according to the present invention is described with referenceto the accompanying drawings.

FIG. 27 illustrates a transmission schematic view of a working vehicle205 to which the transmission structure 9 according to this embodimentis applied.

FIG. 28 illustrates a partial vertical cross-sectional side view of theworking vehicle 205.

In the figures, the same components as those in Embodiments describedabove are designated by the same reference numerals and a descriptionthereof is omitted as appropriate.

The transmission structure 9 according to this embodiment is common tothe transmission structure 8 according to Embodiment 8 described abovein the point of having the output side first to third clutch mechanisms80(1) to 80(3).

Meanwhile, the transmission structure 9 is different from thetransmission structure 8 according to Embodiment 8 described above inthe following point.

More specifically, the transmission structure 8 according to Embodiment8 described above is configured so that the rotation power istransmitted to the traveling transmission shaft 235 through theforward/reverse movement switching mechanism 230 in all the first tothird transmission states developed according to the engagement statesof the output side first to third clutch mechanisms 80(1) to 80(3).

In contrast thereto, the transmission structure 9 according to thisembodiment is configured so that, while the rotation power istransmitted to the traveling transmission shaft 235 through theforward/reverse movement switching mechanism 230 in the first and secondtransmission states developed according to the engagement states of theoutput side first and second clutch mechanisms 80(1) and 80(2), therotation power in the forward movement direction is transmitted to thetraveling transmission shaft 235 without via the forward/reversemovement switching mechanism 230 in the third transmission statedeveloped in the engagement state of the output side third clutchmechanism 80(3).

In detail, as illustrated in FIG. 27 , the transmission structure 9 isprovided with the HST 10 and the planetary gear mechanism 30, the inputside first transmission mechanism 750(1) capable of operativelytransmitting the rotation power of the driving source 210 to the firstelement (the internal gear 36 in this embodiment) at the input sidefirst speed change ratio and the input side second transmissionmechanism 750(2) capable of operatively transmitting the rotation powerof the driving source 210 to the second element (the carrier 38 in thisembodiment) at the input side second speed change ratio, the input sidefirst and second clutch mechanisms 60(1) and 60(2), the speed changeoutput shaft 45 and the traveling transmission shaft 235, theforward/reverse movement switching mechanism 230, an output side firsttransmission mechanism 770(1) capable of operatively transmitting therotation power of the second element at the output side first speedchange ratio to the speed change output shaft 45, an output side secondtransmission mechanism 770(2) capable of operatively transmitting therotation power of the first element at the output side second speedchange ratio to the speed change output shaft 45, an output side thirdtransmission mechanism 770(3) capable of operatively transmitting therotation power of the first element as the driving force in the forwardmovement direction to the traveling transmission shaft 235, the outputside first to third clutch mechanisms 80(1) to 80(3), the speed changeoperation member 90, the HST sensor 95 a, and the control device 100.

As illustrated in FIG. 27 and FIG. 28 , the transmission structure 9further has the speed change intermediate shaft 43 coupled with thesecond element (the carrier 38 in this embodiment) so as not to berelatively rotatable around the axis.

Moreover, the transmission structure 9 has an output sensor 95 bdirectly or indirectly detecting the rotational speed of the travelingtransmission shaft 235.

The input side first transmission mechanism 750(1) has an input sidefirst driving gear 752(1) relatively rotatably supported by the maindriving shaft 212 operatively coupled with the driving source 210 and aninput side first driven gear 754(1) operatively coupled with the inputside first driving gear 752(1) and the first element (the internal gear36 in this embodiment) in a state of being relatively rotatablysupported by the speed change intermediate shaft 43.

The input side second transmission mechanism 750(2) has an input sidesecond driving gear 752(2) relatively rotatably supported by the maindriving shaft 212 and an input side second driven gear 754(2)operatively coupled with the input side second driving gear 752(2) in astate of being supported by the speed change intermediate shaft 43 so asnot to be relatively rotatable, in which the rotation power of the maindriving shaft 212 is operatively transmitted to the second element (thecarrier 38 in this embodiment) through the speed change intermediateshaft 43.

In this case, as illustrated in FIG. 27 and FIG. 28 , the input sidefirst and second clutch mechanisms 60(1) and 60(2) are supported by themain driving shaft 212 so as to engage/disengage the input side firstand second driving gears 752(1) and 752(2), respectively, with/from themain driving shaft 212.

More specifically, in this embodiment, the input side first clutchmechanism 60(1) is configured to have the input side clutch housing 62supported by the main driving shaft 212 so as not to be relativelyrotatable, an input side first friction plate group 64(1) containing afirst driving side friction plate supported by the input side clutchhousing 62 so as not to be relatively rotatable and a first driven sidefriction plate supported by the input side first driving gear 752(1) soas not to be relatively rotatable in a state of being opposed to thefirst driving side friction plate, and an input side first piston (notillustrated) frictionally engaging the input side first friction plategroup 64(1).

The input side second clutch mechanism 60(2) is configured to have theinput side clutch housing 62, an input side second friction plate group64(2) containing a second driving side friction plate supported by theinput side clutch housing 62 so as not to be relatively rotatable and asecond driven side friction plate supported by the input side seconddriving gear 752(2) so as not to be relatively rotatable in a state ofbeing opposed to the second driving side friction plate, and an inputside second piston (not illustrated) frictionally engaging the inputside second friction plate group 64(2).

In this embodiment, the output side first transmission mechanism 770(1)is configured to be able to operatively transmit the rotation power ofthe second element to the speed change output shaft 45 utilizing theinput side second driven gear 754(2) in the input side secondtransmission mechanism 750(2).

In detail, as illustrated in FIG. 27 and FIG. 28 , the output side firsttransmission mechanism 770(1) has an output side first driven gear774(1) operatively coupled with the input side second driven gear 754(2)in a state of being relatively rotatably supported by the speed changeoutput shaft 45.

The output side second transmission mechanism 770(2) is configured to beable to operatively transmit the rotation power of the first element tothe speed change output shaft 45 utilizing the input side first drivengear 754(2) in the input side first transmission mechanism 750(1).

In detail, as illustrated in FIG. 27 and FIG. 28 , the output sidesecond transmission mechanism 770(2) has an output side second drivengear 774(2) operatively coupled with the input side first driven gear754(1) in a state of being relatively rotatably supported by the speedchange output shaft 45.

In this case, as illustrated in FIG. 27 and FIG. 28 , the output sidefirst and second clutch mechanisms 80(1) and 80(2) are supported by thespeed change output shaft 45 so as to engage/disengage the output sidefirst and second driven gears 774(1) and 774(2), respectively, with/fromthe speed change output shaft 45.

More specifically, in this embodiment, the output side first clutchmechanism 80(1) is configured to have an output side clutch housing 82supported by the speed change output shaft 45 so as not to be relativelyrotatable, an output side first friction plate group 84(1) containing afirst driving side friction plate supported by the output side firstdriven gear 774(1) so as not to be relatively rotatable and a firstdriven side friction plate supported by the output side clutch housing82 so as not to be relatively rotatable in a state of being opposed tothe first driving side friction plate, and an output side first piston(not illustrated) frictionally engaging the output side first frictionplate group 84(1).

The output side second clutch mechanism 80(2) is configured to have theoutput side clutch housing 82, an output side second friction plategroup 84(2) containing a second driving side friction plate supported bythe output side second driven gear 774(2) so as not to be relativelyrotatable and a second driven side friction plate supported by theoutput side clutch housing 82 so as not to be relatively rotatable in astate of being opposed to the second driving side friction plate, and anoutput side second piston (not illustrated) frictionally engaging theoutput side second friction plate group 84(2).

In the output side third transmission mechanism 770(3), the speed changeratio is set so that the rotational speed of the traveling transmissionshaft 235 at the timing when the rotation power of the first element isoperatively transmitted to the traveling transmission shaft 235 throughthe output side third transmission mechanism 770(3) is higher than therotational speed of the traveling transmission shaft 235 at the timingwhen the rotation power of the first element is operatively transmittedto the traveling transmission shaft 235 through the output side secondtransmission mechanism 770(2) and the forward/reverse movement switchingmechanism 230 in the forward movement transmission state.

In this embodiment, the output side third transmission mechanism 770(3)is configured to be able to operatively transmit the rotation power ofthe first element to the traveling transmission shaft 235 utilizing theoutput side second driven gear 774(2) in the output side secondtransmission mechanism 770(2).

In detail, as illustrated in FIG. 27 and FIG. 28 , the output side thirdtransmission mechanism 770(3) has an output side third driven gear774(3) operatively coupled with the output side second driven gear774(2) in a state of relatively rotatably being supported by thetraveling transmission shaft 235.

In this case, as illustrated in FIG. 27 and FIG. 28 , the output sidethird clutch mechanism 80(3) is supported by the traveling transmissionshaft 235 so as to engage/disengage the output side third driven gear774(3) with/from the traveling transmission shaft 235.

More specifically, in this embodiment, the output side third clutchmechanism 80(3) is configured to have the output side clutch housing 83supported by the traveling transmission shaft 235 so as not to berelatively rotatable, an output side third friction plate group 84(3)containing a third driving side friction plate supported by the outputside third driven gear 774(3) so as not to be relatively rotatable and athird driven side friction plate supported by the output side clutchhousing 83 so as not to be relatively rotatable in a state of beingopposed to the third driving side friction plate, and an output sidethird piston (not illustrated) frictionally engaging the output sidethird friction plate group 84(3).

The output side third driven gear 774(3) can also be operatively coupledwith the output side first driven gear 774(1) in place of the outputside second driven gear 774(2).

More specifically, the output side third transmission mechanism 770(3)can also be modified so as to operatively transmit the rotation power ofthe first element to the traveling transmission shaft 235 utilizing theoutput side first driven gear 774(1) in the output side firsttransmission mechanism 770(1).

FIG. 29 illustrates a graph illustrating the relationship between thetraveling vehicle speed and the HST output in the working vehicle 205 towhich the transmission structure 9 according to this embodiment isapplied.

As illustrated in FIG. 29 , the control device 100 in this embodiment

-   operates the output adjustment member 20 so that the HST output is    set to the first HST speed setting the synthetic rotation power of    the planetary gear mechanism 30 to zero in response to an operation    to the zero speed position of the speed change operation member 90,-   when the speed change operation member 90 is operated in a forward    movement side low speed range between the zero speed position and    the forward movement side first switching speed position, while the    control device 100 develops a first transmission state where the    first element is functioned as the reference power input portion    operatively transmitted from the driving source 210 and the second    element is functioned as the output portion of synthetic rotation    power, so that the synthetic rotation power output from the second    element is operatively transmitted to the speed change output shaft    45 by bringing the output side first clutch mechanism 80(1) into the    engagement state and bringing the other output side clutch    mechanisms 80(2) and 80(3) into the disengagement state while    bringing the input side first clutch mechanism 60(1) into the    engagement state and bringing the input side second clutch mechanism    60(2) into the disengagement state, the control device 100 brings    the forward/reverse movement switching mechanism 230 into the    forward movement transmission state and the control device 100    operates the output adjustment member 20 so that the HST output is    speed-changed from the side of the first HST speed toward the side    of the second HST speed in response to the acceleration operation of    the speed change operation member 90,-   when the speed change operation member 90 is operated in a forward    movement side intermediate speed range between the forward movement    side first switching speed position and the forward movement side    second switching speed position, while the control device develops a    second transmission state where the second element is functioned as    the reference power input portion and the first element is    functioned as the output portion of synthetic rotation power, so    that the synthetic rotation power output from the first element is    operatively transmitted to the speed change output shaft 45 by    bringing the output side second clutch mechanism 80(2) into the    engagement state and bringing the other output side clutch    mechanisms 80(1) and 80(3) into the disengagement state while    bringing the input side first clutch mechanism 60(1) into the    disengagement state and bringing the input side second clutch    mechanism 60(2) into the engagement state, the control device 100    brings the forward/reverse movement switching mechanism 230 into the    forward movement transmission state and the control device 100    operates the output adjustment member 20 so that the HST output is    speed-changed from the side of the second HST speed toward the side    of the first HST speed in response to the acceleration operation of    the speed change operation member 90,-   when the speed change operation member 90 is operated in a forward    movement side high speed range beyond the forward movement side    second switching speed position, while the control device 100    develops a third transmission state where the second element is    functioned as the reference power input portion and the first    element is functioned as the output unit of synthetic rotation    power, so that the synthetic rotation power output from the first    element is operatively transmitted to the traveling transmission    shaft 235 as driving force in the forward movement direction through    the output side third transmission mechanism 770(3) by bringing the    output side third clutch mechanism 80(3) into the engagement state    and bringing the other output side clutch mechanisms 80(1) and 80(3)    into the disengagement state while bringing the input side first    clutch mechanism 60(1) into the disengagement state and bringing the    input side second clutch mechanism 60(2) into the engagement state,    the control device 100 operates the output adjustment member 20 so    that the HST output is speed-changed from the side of the second HST    speed toward the side of the first HST speed in response to the    acceleration operation of the speed change operation member 90,-   when the speed change operation member 90 passes a forward movement    side second switching speed position between the forward movement    side intermediate speed range and the forward movement side high    speed range, the control device 100 operates the output adjustment    member 20 so that the rotational speed of the traveling transmission    shaft 235 in a transmission state developed immediately after the    passage coincides with or approaches the rotational speed of the    traveling transmission shaft 235 in a transmission state developed    immediately before the passage,-   when the speed change operation member 90 is operated in a reverse    movement side low speed range between the zero speed and a reverse    movement side first switching speed position, while the control    device 100 develops the first transmission state, the control device    brings the forward/reverse movement switching mechanism 230 into the    reverse movement transmission state and the control device 100    operates the output adjustment member 20 so that the HST output is    speed-changed from the side of the first HST speed toward the side    of the second HST speed in response to the acceleration operation of    the speed change operation member 90, and-   when the speed change operation member 90 is operated in a reverse    movement side high speed range beyond the reverse movement side    first switching speed position, while the control device 100    develops the second transmission state, the control device 100    brings the forward/reverse movement switching mechanism 230 into the    reverse movement transmission state and the control device 100    operates the output adjustment member 20 so that the HST output is    speed-changed from the side of the second HST speed toward the side    of the first HST speed in response to the acceleration operation of    the speed change operation member 90.

In the same manner as in Embodiment 1, the input side first speed changeratio of the input side first transmission mechanism 750(1) and thesecond speed change ratio of the input side second transmissionmechanism 750(2) are set so that the rotational speed of the secondelement (the carrier 38 in this embodiment) when the HST output is setto the second HST speed in the first transmission state and therotational speed of the second element by the rotation power transmittedthrough the input side second transmission mechanism 750(2) in thesecond transmission state are the same and so that the rotational speedof the first element (the internal gear 36 in this embodiment) when theHST output is set to the second HST speed in the second transmissionstate and the rotational speed of the first element by the rotationpower transmitted through the input side first transmission mechanism750(1) in the first transmission state are the same.

As illustrated in FIG. 29 , the output side first speed change ratio ofthe output side first transmission mechanism 770(1) and the output sidesecond speed change ratio of the output side second transmissionmechanism 770(2) are set so that the rotational speed developed in thespeed change output shaft 45 when the HST output is set to the secondHST speed is same in the first and second transmission states.

Then, as described above, when the speed change operation member 90passes the forward movement side second switching speed position betweenthe forward movement side intermediate speed range and the forwardmovement side high speed range, the control device 100 operates theoutput adjustment member 20 so that the rotational speed of thetraveling transmission shaft 235 in a transmission state developedimmediately after the passage coincides with or approaches therotational speed of the traveling transmission shaft 235 in atransmission state developed before the passage.

More specifically, when the speed change operation member 90 is operatedin the acceleration direction in the forward movement side intermediatespeed range (second transmission state), passes the forward movementside second switching speed position, and then enters the forwardmovement side high speed range, while the control device 100 shifts theoutput side second clutch mechanism 80(2) from the engagement state tothe disengagement state and shifts the output side third clutchmechanism 80(3) shifted from the disengagement state to the engagementstate to perform switching from the second transmission state to thethird transmission state, the control device 100 operates the outputadjustment member 20 so that the output of the HST 10 is speed-changedfrom the rotational speed (first HST speed) setting the travelingvehicle speed to +b under the second transmission state to therotational speed (third HST speed) setting the traveling vehicle speedto +b or speed therearound under the third transmission state.

When the speed change operation member 90 is operated in thedeceleration direction in the forward movement side high speed range(third transmission state), passes the forward movement side secondswitching speed position, and then enters the forward movement sideintermediate speed range, while the control device 100 shifts the outputside third clutch mechanism 80(3) from the engagement state to thedisengagement state and shifts the output side second clutch mechanism80(2) from the disengagement state to the engagement state to performswitching from the third transmission state to the second transmissionstate, the control device 100 operates the output adjustment member 20so that the output of the HST 10 is speed-changed from the rotationalspeed (third HST speed) setting the traveling vehicle speed to +b underthe third transmission state to the rotational speed (first HST speed)setting the traveling vehicle speed to +b or speed therearound under thesecond transmission state.

The transmission structure 9 having such a configuration can furtherextend the speed changeable range (speed change region) on the forwardmovement side while obtaining the same effects as those of thetransmission structure 1 according to Embodiment 1.

In this embodiment, the output side first and second speed change ratiosare set so that the traveling vehicle speed when the HST output is setto the second HST speed is same in the first and second transmissionstates as described above. However, in place of the setting, aconfiguration may be acceptable in which the control device 100 operatesthe output adjustment member 20 so that, in the switching between thefirst and second transmission states, the traveling vehicle speed in atransmission state after the switching coincides with or approaches thetraveling vehicle speed in the transmission state after the switching.

The transmission structure 9 according to this embodiment is housed in ahousing structure 500B in the working vehicle 205.

As illustrated in FIG. 28 , the housing structure 500B is provided witha hollow housing body 505B, a first bearing plate 516B detachablycoupled with the hollow housing body 505B, and a second bearing plate554B detachably coupled with the housing body 505B at a position spacedfrom the first bearing plate 516B in the longitudinal direction of thehousing body 505B and forming a partitioned space S between the firstbearing plates 516B and the second bearing plate 554B.

In this embodiment, the housing body 505B has a front housing body 510Band a rear housing body 550B detachably connected in series.

The first bearing plate 516B is detachably coupled with a boss portion511 provided in the inner surface of the front housing body 510B near arear opening of the front housing body 510B and the second bearing plate554B is detachably coupled with a boss portion 551 provided in the innersurface of the rear housing body 550B near a front opening of the rearhousing body 550B.

As illustrated in FIG. 28 , the main driving shaft 212, the speed changeintermediate shaft 43, the speed change output shaft 45, and thetraveling transmission shaft 235 are supported by the first and secondbearing plates 516B and 554B in a state of being parallel to one anotherand disposed along the longitudinal direction of the housing body 505B.

The input side first and second driving gears 752(1) and 752(2) and theinput side first and second clutch mechanisms 60(1) and 60(2) aresupported in a portion located in the partitioned space S of the maindriving shafts 212 in a state where the input side first and secondclutch mechanisms 60(1) and 60(2) are located between the input sidefirst and second driving gears 752(1) and 752(2) with respect to theaxial direction of the main driving shaft 212.

The input side first and second driven gears 754(1) and 754(2) aresupported in a portion located in the partitioned space S of the speedchange intermediate shaft 43 in a state of being located at the samepositions as those of the input side first and second driving gears752(1) and 752(2), respectively, with respect to the axial direction.

The output side first and second driven gears 774(1) and 774(2) and theoutput side first and second clutch mechanisms 80(1) and 80(2) aresupported in a portion located in the partitioned space S of the speedchange output shaft 45 in a state where the output side first and seconddriven gears 774(1) and 774(2) are located at the same positions asthose of the input side second and first driven gears 754(2) and 754(1),respectively, with respect to the axial direction and the output sidefirst and second clutch mechanisms 80(1) and 80(2) are located betweenthe input side first and second driven gears 774(1) and 774(2) withrespect to the axial direction.

The output side third driven gear 774(3) and the output side thirdclutch mechanism 80(3) are supported in a portion located in thepartitioned space S of the traveling transmission shaft 235 in a statewhere the output side third driven gear 774(3) is located at the sameposition in the axial direction as that of the output side second drivengear 774(2) and the output side third clutch mechanism 80(3) is locatedon the far side of the output side second driven gear 774(2) from theoutput side first and second clutch mechanisms 80(1) and 80(2) withrespect to the axial direction.

The forward/reverse movement switching mechanism 230 is supported in aportion located outside the partitioned space S of the speed changeoutput shaft 45 and the traveling transmission shaft 235.

In detail, as illustrated in FIG. 27 and FIG. 28 , the forward/reversemovement switching mechanism 230 has a forward movement side gear train710F containing a forward movement side driving gear 711F supported bythe speed change output shaft 44 and a forward movement side driven gear712F supported by the traveling transmission shaft 235 and meshed withthe forward movement side driving gear 711F, a reverse movement sidegear train 710R containing a reverse movement side driving gear 231Rsupported by the speed change output shaft 45 and a reverse movementside driven gear 712R supported by the traveling transmission shaft 235and meshed with the reverse movement side driving gear 711R through anidle gear 713 (see FIG. 27 ), a forward movement side clutch mechanism720F engaging/disengaging the power transmission in the forwarddirection from the speed change output shaft 45 to the travelingtransmission shaft 235 through the forward movement side gear train710F, and a reverse movement side clutch mechanism 720Rengaging/disengaging the power transmission in the reverse movementdirection from the speed change output shaft 45 to the travelingtransmission shaft 235 through the reverse movement side gear train710R.

As illustrated in FIG. 28 , in this embodiment, the forward movementside driving gear 711F is supported in a rear portion extended rearwardrelative to the second bearing plate 554B of the speed change outputshaft 45 so as not to be relatively rotatable and the reverse movementside driving gear 711R is supported in a rear portion of the speedchange output shaft 45 so as not to be relatively rotatable at aposition spaced from the forward movement side driving gear 711F in theaxial direction.

In this embodiment, the speed change output shaft 45 has a first speedchange output shaft 45 a located on the front side and a second speedchange output shaft 45 b located on the rear side and coupled coaxiallywith the first speed change output shaft 45 a so as not to be relativelyrotatable around the axis, in which the second speed change output shaft45 b forms the rear portion of the speed change output shaft 45.

The forward movement side driven gear 712F is relatively rotatablysupported in a rear portion extended rearward relative to the secondbearing plate 554B of the traveling transmission shaft 235 at the sameposition as that of the forward movement side driving gear 711F withrespect to the axial direction.

The reverse movement side driven gear 712R is relatively rotatablysupported in a rear portion of the traveling transmission shaft 235 atthe same position as that of the reverse movement side driving gear 711Rwith respect to the axial direction.

Then, the forward movement side and reverse movement side clutchmechanisms 720F and 720R are supported in the rear portion of thetraveling transmission shaft 235 in a state of being located between theforward movement side driven gear 712F and the reverse movement sidedriven gear 712R with respect to the axial direction.

In this embodiment, the traveling transmission shaft 235 has a firsttraveling transmission shaft 235 a located on the front side and asecond traveling transmission shaft 235 b located on the rear side andcoupled coaxially with the first traveling transmission shaft 235 a soas not to be relatively rotatable around the axis, in which the secondtraveling transmission shaft 235 b forms the rear portion of thetraveling transmission shaft 235.

By having such a housing structure, the transmission structure 9according to this embodiment can effectively achieve a reduction in thenumber of used gears and the size.

As described above, in this embodiment, the output side third drivengear 774(3) is located at the same position as that of the output sidesecond driven gear 774(2) with respect to the axial direction and ismeshed with the output side second driven gear 774(2).

In place of the configuration, the output side third driven gear 774(3)may be located at the same position as that of the output side firstdriven gear 774(1) with respect to the axial direction and meshed withthe output side first driven gear 774(1). In this case, the output sidethird clutch mechanism 80(3) is supported in a portion located in thepartitioned space S of the traveling transmission shaft 235 in a stateof being located on the far side of the output side first driven gear774(1) from the output side first and second clutch mechanisms 80(1) and80(2) with respect to the axial direction.

As illustrated in FIG. 28 , in this embodiment, a rotary joint 68 forsupplying/discharging hydraulic oil to the input side first and secondclutch mechanisms 60(1) and 60(2) is provided in the main driving shaft212 and a bearing portion of the main driving shaft 212 in the secondbearing plate 554B.

Moreover, a rotary joint 88 for supplying/discharging hydraulic oil tothe output side first and second clutch mechanisms 80(1) and 80(2) isprovided in the speed change output shaft 45 and a bearing portion ofthe speed change output shaft 45 in the first bearing plate 516B.

Furthermore, a rotary joint 238 for supplying/discharging hydraulic oilto/from the output side third clutch mechanism 80(3), the forwardmovement side clutch mechanism 720F, and the reverse movement sideclutch mechanism 720R is provided in the traveling transmission shaft235 and a relay cylinder portion 555 mounted in the second bearing plate554B.

The invention claimed is:
 1. A transmission structure interposed in atraveling system transmission path from a driving source until atraveling device of a vehicle, the transmission structure comprising: anHydrostatic Transmission (HST) configured to continuously changerotation power operatively input from the driving source to rotationpower at least between a first HST speed and a second HST speed; aplanetary gear mechanism having first, second and third elements, inwhich the third element functions as an input portion of the HST output;an input side first transmission mechanism operatively coupled with thefirst element and capable of inputting the rotation power from thedriving source; an output side first transmission mechanism operativelycoupled with the second element and capable of outputting the rotationpower to the traveling device; an input side second transmissionmechanism operatively coupled with the second element and capable ofinputting the rotation power from the driving source; an output sidesecond transmission mechanism operatively coupled with the first elementand capable of outputting the rotation power to the traveling device; aspeed change operation member capable of setting a traveling speed in aforward movement; and a control device performing operation control ofthe HST, the input side first and second transmission mechanisms and theoutput side first and second transmission mechanisms upon receipt of asignal from the speed change operation member, wherein when the speedchange operation member is positioned at a zero speed position, thecontrol device controls the HST so that the HST output has the first HSTspeed that brings the planetary gear mechanism into a synthetic rotationpower zero speed state while developing a first transmission state wherethe first element functions as an input portion of the rotation powerfrom the driving source and the second element functions as an outputportion of outputting rotation power to the traveling device by bringingthe input side first transmission mechanism and the output side firsttransmission mechanism into an engagement state and bringing the inputside second transmission mechanism and the output side secondtransmission mechanism into a disengagement state, wherein when thespeed change operation member is operated in a range from the zero speedposition to a first traveling speed in the forward movement, the controldevice operates the HST so that the HST output is speed-changed from thefirst HST speed toward the second HST speed in response to anacceleration operation in the forward movement of the speed changeoperation member while developing the first transmission state, whereinwhen the speed change operation member is operated in a range from thefirst traveling speed to a second traveling speed in the forwardmovement, the control device operates the HST so that the HST output isspeed-changed from the second HST speed toward the first HST speed inresponse to an acceleration operation in the forward movement of thespeed change operation member while developing a second transmissionstate where the first element functions as the output portion ofoutputting rotation power to the traveling device and the second elementfunctions as the input portion of the rotation power from the drivingsource by bringing the input side first transmission mechanism and theoutput side first transmission mechanism into a disengagement state andbringing the input side second transmission mechanism and the outputside transmission mechanism into an engagement state, and wherein speedchange ratios of the input side first and second transmission mechanismsare set so that when the HST output has the second HST speed, therotational speeds developed in the second elements in the first andsecond transmission states substantially coincides with each other andthe rotational speeds developed in the first elements in the first andsecond transmission states substantially coincides with each other. 2.The transmission structure according to claim 1, wherein speed changeratios of the output side first and second transmission mechanisms areset so that when the HST output has the second HST speed, the rotationalspeeds developed in the traveling device in the first and secondtransmission states substantially coincides with each other.
 3. Thetransmission structure according to claim 2, wherein in a switchingtransition stage between the first and second transmission states, thecontrol device develop a double transmission state in which both theinput side first and second transmission mechanisms are brought into theengagement state and both the output side first and second transmissionmechanisms are brought into the engagement state.
 4. The transmissionstructure according to claim 1, wherein in switching between the firstand second transmission states, the control device operates the HST sothat rotational speed developed in the traveling device in atransmission state after the switching substantially coincides withrotational speed developed in the traveling device in a transmissionstate before the switching.
 5. The transmission structure according toclaim 1, wherein the input side first and second transmission mechanismsand the output side first and second transmission mechanisms eachinclude a clutch unit, and wherein at least one of the input side clutchunits and at least one of the output side clutch units are configured asa hydraulic friction plate type in which a clutch engagement state isdeveloped through a sliding engagement state by receiving pressure oilsupply.
 6. The transmission structure according to claim 5, furthercomprising: a pressure oil supply line receiving pressure oil supplyfrom a hydraulic source; first and second supply/discharge linessupplying/discharging pressure oil to the input side and output sideclutch units of the hydraulic friction plate type, respectively; firstand second electromagnetic valves which are interposed in the first andsecond supply/discharge lines, respectively, and which can take adischarge position where a corresponding supply/discharge line isdrained and a supply position where a corresponding supply/dischargeline is fluid-connected to the pressure oil supply line; and a clutchengagement detection unit detecting an engagement state of the clutchunits of the hydraulic friction plate type, wherein when in switchingbetween the first and second transmission states, the control devicemoves the electromagnetic valve located at the discharge position attime before the switching from the discharge position to the supplyposition while maintaining the electromagnetic valve located at thesupply position at the time before the switching at the supply positionin the switching between the first and second transmission states, andthen moves the electromagnetic valve located at the supply position atthe time before the switching from the supply position to the dischargeposition when the control device recognizes that the clutch unit towhich pressure oil is supplied through the electromagnetic valve, aposition of which is moved from the discharge position to the supplyposition, is brought into the engagement state based on a signal fromthe clutch engagement detection unit.
 7. The transmission structureaccording to claim 1 further comprising: a speed change output shaftoperatively receiving rotation power from the output side first andsecond transmission mechanisms; a traveling transmission shaftoperatively coupled with the traveling device; and a forward/reversemovement switching mechanism disposed between the speed change outputshaft and the traveling transmission shaft.
 8. The transmissionstructure according to claim 1 further comprising: a speed change outputshaft operatively coupled with the traveling device; and a reversemovement transmission mechanism capable of operatively transmitting therotation power of the second element to the speed change output shaft ina reverse rotation state, wherein the output side first and secondtransmission mechanisms are capable of operatively transmitting therotation power of the second element and the first element,respectively, to the speed change output shaft in a normal rotationstate, wherein the speed change operation member is capable of beingfurther operated from the zero speed position toward a rearward movementside, and wherein when the speed change operation member is operatedfrom the zero speed position toward the rearward movement side, thecontrol device operates the HST so that the HST output is speed-changedfrom the first HST speed toward the second HST speed in response to anacceleration operation in the rearward movement of the speed changeoperation member while bringing the input side first transmissionmechanism and the reverse movement transmission mechanism into anengagement state and bringing the input side second transmissionmechanism and the output side first and second transmission mechanismsinto a disengagement state.
 9. The transmission mechanism according toclaim 2 further comprising: a speed change output shaft operativelycoupled with the traveling device; and an output side third transmissionmechanism capable of operatively transmitting the rotation power of thefirst element to the speed change output shaft in parallel with theoutput side second transmission mechanism, wherein the output side firstand second transmission mechanisms operatively rotating the speed changeoutput shaft at output side first and second speed change ratios,respectively, and the output side third transmission mechanismoperatively rotating the speed change output shaft at an output sidethird speed change ratio higher than the output side second speed changeratio, wherein the speed change operation member is capable to be alsooperated in a range between the second traveling speed and a thirdtraveling speed beyond the second traveling speed in the forwardmovement, wherein when the speed change operation member is operated inthe range between the second and third traveling speeds, the controldevice operates the HST so that the HST output is speed-changed from thesecond HST speed toward the first HST speed in response to anacceleration operation in the forward movement of the speed changeoperation member while developing a third transmission state where thefirst element functions as the output portion of outputting rotationpower to the speed change output shaft and the second element functionsas the input portion of the rotation power from the driving source bybringing the input side first transmission mechanism into adisengagement state, bringing the input side second transmissionmechanism into an engagement state, bringing the output side thirdtransmission mechanism into an engagement state and bringing otheroutput side transmission mechanisms into a disengagement state, andwherein in switching between the second and third transmission states,the control device operates the HST so that rotational speed developedin the speed change output shaft in a transmission state after theswitching substantially coincides with rotational speed developed in thespeed change output shaft in a transmission state before the switching.10. The transmission mechanism according to claim 7 further comprisingan output side third transmission mechanism operatively coupled with thefirst element and capable of outputting the rotation power to thetraveling transmission shaft in such a manner that the travelingtransmission shaft rotates in the same rotational direction as the speedchange output shaft, wherein the output side first and secondtransmission mechanisms have output side first and second speed changeratios, respectively, and the output side third transmission mechanismhas an output side third speed change ratio higher than the output sidesecond speed change ratio, wherein the speed change operation member iscapable to be also operated in a range between the second travelingspeed and a third traveling speed in the forward movement, wherein whenthe speed change operation member is operated in the range between thesecond and third traveling speeds, the control device operates the HSTso that the HST output is speed-changed from the second HST speed towardthe first HST speed in response to an acceleration operation in theforward movement of the speed change operation member while developing athird transmission state where rotation power of the first element isoperatively transmitted to the speed change output shaft and the secondelement functions as the input portion of the rotation power from thedriving source by bringing the input side first transmission mechanisminto a disengagement state, bringing the input side second transmissionmechanism into an engagement state, bringing the output side thirdtransmission mechanism into an engagement state and bringing otheroutput side transmission mechanisms into a disengagement state, andwherein in switching between the second and third transmission states,the control device operates the HST so that rotational speed developedin the speed change output shaft in a transmission state after theswitching substantially coincides with rotational speed developed in thespeed change output shaft in a transmission state before the switching.11. A transmission structure comprising: an Hydrostatic Transmission(HST) continuously changing rotation power operatively input into a pumpshaft from a driving source to rotation power at least between first HSTspeed and second HST speed according to an operation position of anoutput adjustment member, and then outputting the changed rotation poweras an HST output from a motor shaft; a planetary gear mechanism havingfirst to third elements, in which the third element functions as aninput portion of the HST output; a speed change output shaft; input sidefirst and second transmission mechanisms capable of operativelytransmitting the rotation power of the driving source to the firstelement and the second element, respectively; input side first andsecond clutch mechanisms engaging/disengaging power transmission of theinput side first and second transmission mechanisms, respectively;forward movement first and second transmission mechanisms capable ofoperatively transmitting rotation power of the second element and thefirst element, respectively, to the speed change output shaft in anormal rotation state; a reverse movement transmission mechanism capableof operatively transmitting the rotation power of the second element tothe speed change output shaft in a reverse rotation state; a forwardmovement first clutch mechanism, a forward movement second clutchmechanism, and a reverse movement clutch mechanism engaging/disengagingpower transmission of the forward movement first transmission mechanism,the forward movement second transmission mechanism, and the reversemovement transmission mechanism, respectively; a speed change operationmember; an HST sensor directly or indirectly detecting a speed changestate of the HST; an output sensor directly or indirectly detectingrotational speed of the speed change output shaft; and a control devicecontrolling operations of the output adjust member, the input side firstclutch mechanism, the input side second clutch mechanism, the forwardmovement first clutch mechanism, the forward movement second clutchmechanism, and the reverse movement clutch mechanism, wherein based ondetection signals of the HST sensor and the output sensor, in a lowspeed state where the rotational speed of the speed change output shaftis from zero speed to speed less than switching speed in a forwardmovement direction, while the control device develops a forward movementfirst transmission state where the input side first clutch mechanism andthe forward movement first clutch mechanism are brought into anengagement state, the control device operates the output adjustmentmember so that the HST output is speed-changed from the first HST speedtoward the second HST speed in response to a forward movement sideacceleration operation of the speed change operation member, in a highspeed state where the rotational speed of the speed change output shaftis equal to or higher than the switching speed in the forward movementdirection, while the control device develops a forward movement secondtransmission state where the input side second clutch mechanism and theforward movement second clutch mechanism are brought into the engagementstate, the control device operates the output adjustment member so thatthe HST output is speed-changed from the first HST speed toward thesecond HST speed in response to the forward movement side accelerationoperation of the speed change operation member, and, in a reversemovement transmission state where the rotational speed of the speedchange output shaft is changed from the zero speed to the reversemovement side, while the control device develops a reverse movementtransmission state where the input side first clutch mechanism and thereverse movement clutch mechanism are brought into the engagement state,the control device operates the output adjustment member so that the HSToutput is speed-changed from the first HST speed toward the second HSTspeed in response to a reverse movement side acceleration operation ofthe speed change operation member.
 12. The transmission structureaccording to claim 11, wherein the input side first transmissionmechanism operatively transmits the rotation power of the driving sourceto the first element at an input side first speed change ratio, whereinthe input side second transmission mechanism operatively transmits therotation power of the driving source to the second element at an inputside second speed change ratio, and wherein the input side first andsecond speed change ratios are set so that rotational speed of thesecond element when the HST output is set to the second HST speed in theforward movement first transmission state and rotational speed of thesecond element by rotation power transmitted through the input sidesecond transmission mechanism in the forward movement secondtransmission state are same and so that rotational speed of the firstelement when the HST output is set to the second HST speed in theforward movement second transmission state and rotational speed of thefirst element by rotation power transmitted through the input side firsttransmission mechanism in the forward movement first transmission stateare same.
 13. The transmission structure according to claim 11, whereinthe forward movement first transmission mechanism operatively transmitsthe rotation power of the second element to the speed change outputshaft at a forward movement first speed change ratio and the forwardmovement second transmission mechanism operatively transmits therotation power of the first element to the speed change output shaft ata forward movement second speed change ratio, and wherein the forwardmovement first and second speed change ratios are set so that rotationalspeed developed in the speed change output shaft when the HST output isset to the second HST speed is same in the first and second transmissionstates.
 14. The transmission structure according to claim 11, whereinthe HST and the planetary gear mechanism are set so that the rotationalspeed of the second element becomes the zero speed when the HST outputis set to the first HST speed in the engagement state of the input sidefirst clutch mechanism.